EXPERIMENTATION OF NEW SPEED REDUCER PROFILES

Transcription

EXPERIMENTATION OF NEW SPEED REDUCER PROFILES SUITABLE
FOR MAXIMUM SPEEDS OF 20 KM/H
Eric EVAIN & Nicolas DUBOS
Ministry for Ecology, Energy, Sustainable Development and Marine Affairs
CETE NC (Technical Research Centre for Normandy and the Central region
of France), France
INTRODUCTION
The Street Code programme was launched by the French Ministry for
Transport in the summer of 2008. Since then a new type of traffic-calming
scheme has been possible: the pedestrian-priority zone.
Speeds within these zones are limited to 20 km/h, the intention being to
prioritise the prevalience of vulnerable users over other road users, who
benefit from effective physical protection. The design of pedestrian-priority
zones must be coherent with this speed restriction.
Despite the fact that the configuration of a pedestrian-priority zone is the key
to ensure that speed limits are being respected, some local road authorities
may be tempted to use physical installations to meet their speed targets. At
the moment speed bumps (such as flat top humps or round top humps) in use
in France are designed to encourage drivers to drive under 30 km/h. Under
the terms of decree 94-447 of 27 May 1994, these speed reducers have to
comply with the NFP 98-300 standard and can only be installed under certain
conditions.
In relation to traffic zones where the intention is to physically compel speeds
below 20 km/h, and to avoid the development of numerous counter-productive
speed reducers, there is a need to define some new speed reducer profiles
(given that the models currently approved are designed to have speeds below
30 km/h).
In addition to this, speed reducers must not become dangerous obstructions
for drivers, nor must their action be excessive for drivers who observe the
speed limits. Therefore a particular attention must be paid to their shape,
dimensions and positioning.
In order to prevent a profusion of unsuitable traffic calming measures, CERTU
(Networks, Transport, Planning and Construction Research Centre) and
CETE NC defined and tested new safe speed reducer profiles suitable for a
20 km/h speed.
LITERATURE REVIEW
The first part of the research was to examine the current state-of-the-art in
order to identify existing techniques for quantifying the physical
aggressiveness of speed reducers.
The purpose of a speed reducer is to create a sensation of discomfort on
vehicle passengers travelling above a determined speed; this in turn acts as
an incentive to approach the obstacle at low speed. However the speedreduction installation must not cause any risk to users.
In order to evaluate a speed reducing accommodation, it is necessary to be
able to quantify and measure the speed reducer’s impact on drivers.
© Association for European Transport and contributors 2010
1
Several studies show that although vehicle passengers’ sensations of
discomfort vis-à-vis speed reducers are highly subjective, as they correlate to
factors that are both internal (psychological) and external (environmental),
they remain nonetheless closely related to the concept of vertical acceleration:
the higher the vertical acceleration, the higher the discomfort. Taking this as a
starting point, a speed reducer needs to generate a vertical acceleration in
order to be uncomfortable, reducing speeds as a consequence.
Vertical acceleration depends not only on the speed used over the bump, but
is also influenced by its shape and dimensions (type, height, length, etc.), as
well as by characteristics intrinsic to the vehicle (mass, suspension, tyre
pressure, type of seat, etc.).
For a speed reducing installation to be effective, vertical acceleration must:
– be low when the installation is crossed at low speed;
– increase sharply close to the design speed;
– not decrease above the design speed;
– be less than 1g (9,81m/s²), as vertical acceleration greater than 1g can
cause tyres to lose contact with the road surface.
The various studies undertaken to establish a relationship between vertical
acceleration and perceived passenger discomfort show that the discomfort
threshold is around 5 m/s², and that in order to run in comfort over a speed
reducer, 85% of drivers adopt a speed that will create an acceleration of less
than 3.35 m/s².
Based on this literature review dedicated to speed reducers, different profiles
were preselected for their geometric features which create vertical
accelerations close to 5 m/s² when crossed at speeds of around 20 km/h.
The selected profiles are as follows:
- speed reducer 1: flat top hump; 4m-long, 10cm high with a 2m-long
plateau;
- speed reducer 2: round top hump; 2.40m-long and 12.5cm-high;
- speed reducer 3: short round top hump (small bump); 50cm-long and
7cm-high.
PURPOSE OF THE EXPERIMENTATION
The purpose of the experimentation was to examine whether the speed
reducer profiles selected after this literature review were suitable in
pedestrian-priority zones, i.e. do drivers cross them at speeds below 20 km/h,
and can they be crossed safely by all types of user?
The following criteria were examined, based on these objectives:
- crossing speed used by motor vehicles;
- differences of driving behaviours according to all types of vehicle
(car, motorcycle, bicycle);
- ability of all types of user to cross the speed reducer easily and
safely;
- speed reducer function (relationship between speed and vertical
acceleration);
- speed reducer comfort.
2
VALIDATING SPEED REDUCER PROFILES
Before the construction of the speed reducers and prior to any in-situ testings,
a dynamic simulation of the selected speed reducer profiles was carried out in
partnership with CETE Lyon, using the CALLAS computerised simulator. The
simulation allowed to confirm that the speed reducers would theoretically
generate a vertical acceleration of around 5 m/s² at 20 km/h.
A previous series of simulations indicated that the flat top hump generated
insufficient vertical accelerations. Its ramp angle (ascending gradient) was
modified to increase the slope: the ramp length was reduced from 1m to
50cm, and the height remained unchanged at 10 cm. This resulted in the
ramp angle rising from 10 to 20%.
Furthermore, the vehicle trim height commonly found on modern cars meant
that the 12.5-cm-high hump was likely to scratch beneath the vehicles as they
would run through it. The height of this speed reducer was therefore lowered
to 10cm, and its length was reduced from 2.40m to 2m in order to maintain a
similar slope.
The table below summarises the theoretical maximum vertical acceleration
values for a vehicle body (vehicle with only one person on board).
Maximum of Vertical Acceleration for each type of car (m/s²)
406
Monospace
SR #1
SR #2
SR #3
SR #1
SR #2
SR #3
Speed (km/h)
SR #1
Clio
SR #2
0
0
0
0
0
0
0
0
0
20
5.28
3.46
3.98
4.57
4.01
3.26
6.37
25
6.05
4.29
4.56
5.59
3.74
4.19
30
7.45
4.79
5.15
6.09
4.09
4.94
35
7.88
5.62
6.15
6.55
4.62
5.8
9.24
40
6.29
7.45
7.09
5.65
50
6.78
* SR = Speed Reducer
9.12
7.69
6.87
SR #3
SR #1
Average
SR #2
0
0
0
0
3.92
4.41
5.41
3.80
3.88
6.4
4.52
5.56
6.01
4.18
4.77
8.07
5.53
6.65
7.20
4.80
5.58
6.53
8.23
7.89
5.59
6.73
6.71
6.87
8.94
7.09
6.27
7.70
8.43
9.07
11.32
7.69
7.57
9.62
SR #3
Table 1: maximum vertical acceleration for the three speed reducers as a function of
crossing speed
The table shows that at 20 km/h (the lowest value for the CALLAS model),
vertical accelerations are close to 5 m/s² and all are greater than 3.35 m/s².
The profiles identified in the literature review were therefore selected for the
experimentations.
The characteristics of the speed reducers finally tested were as follows:
Speed reducer 1
Speed reducer 2
Speed reducer 3
3m flat top hump;
2m round top hump;
small bump;
10cm-high with a
10 cm-high
50 cm-long and
2m-long plateau
7 cm-high
3
PERFORMING THE TESTINGS
The testings concerned both motorist (light vehicles, powered two-wheelers,
and buses) and non-motorist users (bicycles, people with restricted mobility).
The first objective was to ensure that the user behaviour observed
corresponded as closely as possible with natural behaviours that would be
encountered in a pedestrian-priority zone.
In order to get a representative sample of driving behaviours, the testings
across the speed reducers were conducted using as many users as possible
rather than having just one or two people responsible for the trials.
In addition, in order to rule out the possible influence of drivers having to
adapt to a new vehicle dedicated to the trials, decision was taken to allow the
panel members to use their own vehicles for the experiment. The second
advantage of this was that drivers would not drive less cautiously their own
cars than they would drive a company car.
Cars
A panel of volunteer subjects was picked up amongst CETE NC staff; a total
of 16 people (8 groups of 2) driving their own cars.
The sequence in which drivers drove over the speed reducers was planned to
avoid their overall impressions being influenced by systematically crossing in
the same order.
Drivers were given the option to complete 2 exercises: a compulsory one and
an optional one.
-
compulsory run: drive their own cars, at free speed, 3 times in a row,
over each speed reducer, then fill in the questionnaire to give their
impressions;
-
optional run (volunteers): cross each speed reducer at a fixed 20km/h.
In order to avoid possible damages to private cars, this exercise was
conducted using a vehicle supplied by CETE NC. After the crossings,
drivers were asked to complete the questionnaire again.
In terms of measured speeds, we considered for the purpose of these trials
that after the 3rd crossing, drivers would have gained an acquaintance of the
speed reducer and in the next run they would cross it at a stable speed that
would not vary by much subsequently.
Motorcycles and scooters
Testings for powered two-wheelers (PTW) were conducted in the same way
as for cars, although for safety reasons riders were not asked to do the
optional exercise.
Bicycles, buses and wheelchair users
The experimentation with cyclists and people with restricted mobility was
aimed at getting impressions after crossing the speed reducers. As this device
is not installed to slow down these categories of road users, no speed
measurements were done.
For buses, the only criterion examined was the capacity for them to run over
the bumps with no damages.
4
TEST RESULTS FOR LIGHT VEHICLES
A – Speed measurements
Expected speeds during the trials were too low (5 to 25 km/h) to allow use of
standard equipments such as radars.
Furthermore, as the testings were carried out with private cars, it was
impossible to fit them with instruments to give a constant log of their speeds.
The solution adopted for logging speeds was to install a STERELA MajorBI
traffic counter close to the speed reducer itself.
Traffic counters generate a time-stamp to log the pulse given by a wheel while
it runs over the rubber tube placed before and/or after the speed reducer.
Experience tells us that measuring speed with a traffic counter is:
- almost impossible for speeds below 5 km/h (the pulse is not strong
enough);
- difficult after the speed reducer: quite often no pulse was logged, even
after moving the tube further away from each of the 3 speed reducers.
For the purpose of these trials therefore, only the speed reducer entrance
speed was taken into account.
The compilation of entrance speeds is shown in the table below.
SR #
Driver
lap 1
lap 2
lap 3
speed 20 km/h
lap 1
free
lap 2
speed
lap 3
speed 20 km/h
lap 1
free
lap 2
speed
lap 3
speed 20 km/h
free
speed
1
2
3
A
21.0
17.9
17.6
15.7
16.4
17.3
14.9
17.9
22.9
23.5
22.4
18.6
B
10.6
11.9
12.4
15.2
12.5
13.2
11.6
15.7
13.2
14.0
14.6
20.2
C
14.1
16.5
14.8
17.8
11.0
15.0
13.9
15.9
13.6
19.8
16.5
16.8
D
20.6
17.1
18.0
18.1
15.2
17.4
15.2
19.3
11.5
16.8
14.6
18.1
E
4.6
4.8
11.5
7.8
10.0
8.6
6.4
F
10.6
12.4
11.9
18.6
10.6
11.7
12.5
20.2
G
15.1
15.6
15.4
21.1
13.1
12.4
12.3
15.0
12.3
8.8
18.2
6.2
14.1
6.2
H
10.2
10.1
11.0
18.2
9.1
10.7
11.7
18.2
10.3
15.1
13.1
19.0
I
9.0
12.6
11.1
13.4
13.4
11.9
13.4
12.7
11.9
12.8
13.4
19.0
J
19.5
17.2
16.9
18.6
16.6
17.9
13.3
15.5
13.3
14.4
13.5
15.2
K
16.5
14.9
16.8
17.4
13.5
13.3
13.7
10.7
14.9
16.2
16.3
L
13.7
13.1
13.5
20.2
12.2
10.6
8.5
19.0
6.7
6.9
6.8
19.8
M
16.0
21.3
20.8
16.0
12.8
16.6
18.7
17.2
10.9
12.5
7.7
11.2
N
14.3
15.3
13.8
22.1
14.1
13.6
14.1
20.2
13.9
13.7
13.9
13.7
O
17.3
14.8
14.3
22.1
14.8
11.5
12.9
8.1
P
12.6
6.8
10.2
25.8
10.6
10.4
13.5
11.9
8.5
6.3
12.0
13.7
Moyenne
14.7
13.9
14.0
18.3
13.0
13.4
13.0
15.4
12.3
13.6
12.8
16.7

3.79
4.20
3.81
3.68
2.75
2.69
2.42
4.06
3.80
5.04
4.36
2.74
Table 2: entrance speeds (km/h) for each speed reducer
Conclusions concerning speed reducer entry speeds
The first observation is that the average of the recorded speeds is below 20
km/h for the three crossings at free speed (compulsory run).
Speeds are almost all below 20 km/h in passage 1. When approaching this
new speed reducer, the subjects think it is aggressive enough to slow down
their speeds when running over it.
Speeds recorded during subsequent passages are below 20 km/h and stable
overall. The discomfort experienced by drivers encourages them not to
increase their speed.
The comparison of the three speed reducers highlights the following
observations:
-
-
speed reducer 1 reduces speeds to acceptable levels, but during the
third passage there remains a wide variance in panel members’
crossing speeds (10 to 18 km/h);
speed reducer 2 reduces speeds still further and, during passage 3,
speeds are essentially between 11 and 15 km/h. In terms of the entry
speed, this speed reducer is the most homogeneous;
5
-
speed reducer 3 operates differently from the other two. During the
first passage, drivers crossed it at the lowest speeds (10 to 14 km/h).
But once drivers became familiar with it, speeds for the second
passage tended to rise; the third passage was notable for the variation
in entry speeds (6 to 17 km/h). This is the speed reducer that produced
the most heterogeneous results.
Figure 1: car running across speed reducer 1
B – Vertical acceleration
Two vehicles fitted with movable instruments were used for testings at speeds
higher than 20 km/h: a 1995 Mk1 Renault Clio and a 1996 Peugeot 306
Estate.
In order to measure vertical accelerations, both vehicles were fitted with a
Xsens Mti 5g inertia logger, with the sensor sticked to the metal of the main
frame.
Figure 2: Inertial logger into the car
The trials occurred as follows: three successive passages over each speed
reducer at the same speed, first in a Peugeot 306 Estate, then a Mk1 Renault
Clio. The speed stages were 5, 10, 15, 20, 25, 30 and 40 km/h.
6
Vertical accelerations were recorded during each passage. The initial
acceleration value is that of the gravitational pull: 9.81 m/s².
Negative acceleration is the decompression phase, where the car gets nearer
to the ground.
Positive acceleration is the extension phase, where the car rises away from
the ground.
25
20
Vertical Acceleration (m/s²)
Negative Maximal Acceleration = - (16,92 - 9,81) = -7.11 m/s²
15
10
9,81
5
Positive Maximal Acceleration = - (2.46 - 9,81) = 7.35 m/s²
0
7
7.5
8
8.5
9
9.5
10
10.5
11
time (s)
Figure 3: vertical acceleration of the Peugeot 306 Estate during crossing
speed reducer 3 at 15 km/h
The following graph shows the relationship between maximum positive
vertical acceleration as a function of the speed reducer entrance speed:
18
17
Peugeot 306
Renault Clio
16
15
Positive Maximal Acceleration (m/s²)
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
Speed (km/h)
Figure 4: maximum positive acceleration as a function of entrance speed,
speed reducer 1.
7
18
17
Peugeot 306
Renault Clio
16
Positive Maximal Acceleration (m/s²) (m/s²)
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
Speed (km/h)
speed reducer 2.
18
17
Peugeot 306
Renault Clio
16
Positive Maximal Acceleration (m/s²) (m/s²)
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
45.00
Speed (km/h)
speed reducer 3.
Conclusions concerning vertical acceleration
Regarding recorded vertical accelerations, and in the light of the reference
threshold values identified in the literature review (5 m/s² as the threshold for
discomfort but 3,35 m/s² and less for speeds used by 85% of drivers), we can
see that:
-
the 5 m/s² vertical acceleration value is reached at a speed of 13 km/h
for speed reducers 1 and 2;
8
-
-
-
-
at 20 km/h, speed reducers 1 and 2 both reach an average value of 8.5
m/s²; this value remains constant up to 40 km/h. Perceived discomfort
does not decrease above 20 km/h;
for speed reducer 3, discomfort is immediate as the lowest vertical
acceleration value logged is 5.4 m/s² at 7 km/h;
vertical acceleration values increase continually across the 5 km/h - 40
km/h speed range, reaching 15 m/s² for speed reducer 3. There is no
step observed with speed reducer 3;
over 23 km/h, all vertical acceleration values for speed reducer 3
exceed 10 m/s², which represents a potential risk to safety. As
indicated in the literature review, the 10 m/s² value is the point beyond
which the tyres may lose contact with the road surface; this loss of
contact is observed in the recorded videos;
the trials cannot be used to determine the speed thresholds that
correspond to a vertical acceleration of 3.35 m/s² as this would require
a significantly higher number of passages.
C – Drivers’ discomfort
Drivers’ impressions when crossing the speed reducers are assessed through
a questionnaire that driver panel subjects completed after their passages.
The questionnaire aims at quantifying the discomfort level perceived by
drivers, their estimated crossing speed as well as their impressions of the
speed reducers dangerosity and slipperiness.
Below is the compilation table of light vehicle drivers feeling.
Speed
Reducer
#1
#2
#3
Intended natural
speed
Level of discomfort at free speed felt by subjects driving
their own cars (lap 1 + 2 + 3)
Level of discomfort at 20km/h felt by subjects driving the
same car (Peugeot 306)
less than more than
Not
Slightly
Very
Not
Slightly
Very
Uncomfortable
Uncomfortable
20 km/h 20 km/h uncomfortable uncomfortable
uncomfortable uncomfortable uncomfortable
uncomfortable
94%
93%
88%
6%
7%
12%
15%
23%
8%
42%
27%
17%
33%
29%
44%
10%
21%
31%
18%
21%
33%
9%
21%
45%
36%
29%
22%
37%
29%
0%
Table 3: compilation of light vehicle drivers feeling
Firstly, feedback from car drivers shows that a large majority of them intended
to cross the speed reducers under 20 km/h, which is confirmed by the
measured speeds.
Regarding discomfort at free speed, 57% of drivers do not consider speed
reducer 1 as uncomfortable, whereas reactions to speed reducer 2 are split
50/50 between uncomfortable and not uncomfortable; 75% of car drivers
found speed reducer 3 uncomfortable.
The first analysis examined discomfort as a function of the type of user, a
process that highlighted certain characteristics of each type of speed reducer.
However analysis of discomfort experienced when crossing the speed
reducers does not include data concerning the real crossing speed. In order to
attempt to establish a closer link between driver impressions after each
passage and the speed of these passages, a correlation was made between
driver discomfort data and vehicle speed. This correlation was used to identify
a speed threshold above which each speed reducer was felt to be
uncomfortable by the majority of drivers.
9
SR
#1
#2
#3
Drivers feeling
Number
Not
Slightly
Very
speed (km/h)
uncomfortable
of drivers uncomfortable uncomfortable
uncomfortable
16%
53%
31%
0%
0 to 16 km/h
32
69%
31%
13%
20%
40%
27%
> 16 kmh/h
15
33%
67%
27%
30%
30%
13%
0 to 15 km/h
32
57%
43%
10%
9%
27%
46%
> 15 kmh/h
15
27%
73%
0%
17%
44%
39%
0 to 15 km/h
23
17%
83%
18%
23%
53%
6%
> 15 kmh/h
15
41%
59%
Table 4: relationship between drivers feeling and crossing speed
In conclusion, for speed reducers 1 and 2 the discomfort experienced
increases at high crossing speeds, whereas for speed reducer 3 the
discomfort felt is less pronounced at higher speeds. Drivers familiar with
speed reducer 3 might tend not to reduce their speed in order to diminish their
discomfort.
Remarks about discomfort
The following conclusions can be drawn from the testings:
- for speed reducers 1 and 2 there is a direct relationship between driver
discomfort and vertical acceleration at speeds of up to 20 km/h;
- for speed reducer 3, the direct relationship between discomfort and
vertical acceleration ceases at speeds above 15 km/h. The discomfort
noted by the panel decreases above 15 km/h even though vertical
acceleration increases.
Thus vertical acceleration may not be the only criterion to take into account
when defining discomfort, as mentioned in the literature review.
D – Crossing ability
All 3 speed reducers may be considered safe to cross without damages on
cars.
TEST RESULTS FOR POWERED TWO-WHEELERS
A – Recorded speeds
Speeds were measured the same way as for light vehicles.
Speed Reducer
lap 1
#1
lap 2
lap 3
lap 1
#2
lap 2
lap 3
lap 1
#3
lap 2
lap 3
A
14.8
13.0
15.2
11.5
B
C
23.4 18.1
22.8
25.6
25.5 19.2
26.8
18.1 20.5
13.7 15.8
18.7 23.7
17.1
D
19.0
16.9
14.8
19.7
22.7
23.6
16.9
19.0
24.6
E
22.6
26.9
29.7
19.5
28.3
22.6
19.5
F
G
H
16.0 21.3 29.6
26.2 25.2 38.1
30.8 21.3
20.5 23.1 16.7
23.4 30.8 33.5
18.2 22.2 28.4
29.8 14.6 19.0
16.0 12.9 40.6
12.8 12.8 27.7
I
21.9
29.1
40.8
26.6
12.7
47.1
14.9
17.0
23.5
J
23.6
54.4
60.4
24.7
43.9
67.9
25.9
49.4
45.3
K
20.8
17.4
22.5
15.4
25.7
23.5
16.4
21.6
25.7
L
14.6
15.3
15.3
13.6
18.2
18.2
15.0
17.7
15.0
M
30.8
30.8
32.9
22.4
29.0
35.2
26.0
29.0
27.4
N
O
27.7 28.3
25.3 20.2
26.6
33.0 20.2
30.5 32.7
36.0 35.4
22.0 17.7
24.8 12.9
Vmoy
22.7
26.0
29.2
21.4
26.5
28.8
14.5
20.5
20.8

4.99
10.47
12.85
5.01
8.31
13.96
2.37
2.77
5.30
Table 5: compilatin of entry speeds (km/h) for each speed reducer
10
Entrance speeds measured for two-wheelers show that:
- average speeds for the third passage are higher than 20 km/h for all
speed reducers;
- average speeds are systematically higher than those recorded by the
light vehicles;
- speed reducer 1 is crossed at the highest speeds;
- speed reducer 2 slows motorcycles more than mopeds.
- speed reducer 3 is the most effective at moderating crossing speed;
- all the speed reducers can be crossed at high speed by certain types of
motorcycle (trial, roadster); maximum entry speeds logged were
between 50 and 70 km/h, depending on the speed reducer.
Figure 7: PTW crossing speed reducer 3
B – Drivers’ feelings
The table below summarises the data gathered for powered two-wheelers.
Intended natural
speed
Speed
Reducer less than more than
Not
Slightly
Very
Uncomfortable
20 km/h 20 km/h uncomfortable uncomfortable
uncomfortable
#1
#2
#3
60.00%
53.33%
86.67%
40.00%
46.67%
13.33%
18.89%
28.88%
2.32%
36.67%
42.22%
11.63%
31.11%
23.33%
25.58%
13.33%
5.55%
60.46%
Skid resistance
Oui
Non
dangerousness
Oui
0.00% 100.00% 20.00%
0.00% 100.00% 20.00%
46.67% 53.33% 73.33%
Non
80.00%
80.00%
26.67%
Table 6: drivers feeling for powered two-wheelers
The driver impression data for powered two-wheelers shows that, although
the majority intends to cross at speeds below 20 km/h, actual averages are in
excess of 20km/h. For example, although 53% of riders intended to make a
third passage over speed reducer 2 at under 20 km/h, only 5 in 16 did, i.e.
31%.
11
Regarding discomfort at free speed, speed reducers 1 and 2 are not judged
uncomfortable by 56% and 71% of riders respectively, whereas 86% of riders
considered speed reducer 3 as uncomfortable.
As the speed/discomfort relationships are relatively different depending on the
speed reducer profile, the analysis of speed versus rider impressions was
performed by type of speed reducer.
Three speed ranges were defined in order to highlight the trends in terms of
discomfort as a function of speed.
SR
#1
#2
#3
Drivers feeling
Number of
Not
Slightly
Very
speed (km/h)
uncomfortable
drivers
uncomfortable uncomfortable
uncomfortable
5%
65%
10%
20%
0 to 20 km/h
10
70%
30%
24%
19%
48%
9%
20 to 30 km/h
21
43%
57%
25%
37%
12%
25%
> 30 kmh/h
8
63%
37%
23%
61%
8%
8%
0 to 20 km/h
13
84%
16%
11%
47%
37%
5%
20 to 30 km/h
19
58%
42%
64%
18%
18%
0%
> 30 kmh/h
11
82%
18%
0%
14%
32%
54%
0 to 20 km/h
22
14%
86%
8%
8%
17%
67%
20 to 30 km/h
12
16%
84%
0%
0%
67%
33%
> 30 kmh/h
3
0%
100%
Table 7: relationship between speed and discomfort for powered two-wheelers
Speed reducers 1 and 2 were not considered to be particularly uncomfortable
regardless of the crossing speed. Therefore, and unlike the case of the light
vehicles, it is impossible to determine a discomfort speed threshold for
powered two-wheelers.
On the other hand, speed reducer 3 is widely judged uncomfortable at all
speeds.
C – crossing ability
With speed reducer 3, some motorcycles suffer wobbling, and there is a
possibility of scratching.
Furthermore, riders told that they could be launched off by speed reducer at
some speed (tyres lose contact with the road surface).
TEST RESULTS FOR CYCLISTS
A – Rider discomfort
As the objective is not to slow down the cyclists, no speeds were recorded.
The panel of 9 cyclists comprised 3 town bikes, 3 hybrids, 1 mountain bike, 1
e-bike and 1 folding bike.
12
After passing three times over each speed reducer, cyclists filled in a
questionnaire to give their impressions about comfort, slipperiness and
dangerousness.
Speed
Reducer
#1
#2
#3
breaking
Yes
No
67%
22%
89%
33%
78%
11%
Skid resistance dangerousness
Not
Slightly
Very
Uncomfortable
Oui
Non
Oui
Non
uncomfortable uncomfortable
uncomfortable
22%
39%
0%
34%
50%
22%
22%
0%
11%
22%
11%
67%
0%
0%
29%
100%
100%
71%
14%
0%
75%
86%
100%
25%
Table 8: impressions of cyclists
Only speed reducer 3 is felt to be dangerous (75%) and uncomfortable (78%)
by cyclists.
B – crossing capacity
Some riders reported that their pedals scratched the crown of speed reducer 3
when crossing over the device, which may cause them to fall.
Some bicycles also suffered wobbling when crossing speed reducer 3.
WHEELCHAIR USERS
Two disabled people tested the speed reducers:
- one person in a manual wheelchair;
- one person in a electric wheelchair.
Note that the ramp angles of the tested speed reducers do not meet French
accessibility standards as defined in the 15 January 2007 decree.
For the manual wheelchair user, all 3 speed reducers were too high and
crossing them demanded considerable physical effort; indeed, speed reducer
3 proved to be unmountable, despite several attempts. Speed reducer 1 offers
the advantage of a central plateau, allowing wheelchair users to re-position
themselves and have some rest before going down the speed reducer. Speed
reducers 1 and 2 are also very steep (20%), leading to a risk of the wheelchair
toppling over and the occupant falling out, both when entering and exiting the
speed reducer.
It is important also to note that the person who undertook the tests declared
himself physically strong, and that if he has trouble travelling over speed
reducers 1 and 2, then less physically strong wheelchair users would struggle
hard to cross them, if they managed at all.
Only speed reducer 3 was hard to cross for the person using the electric
wheelchair. But, in addition to the risk of tipping over, the steep ramp angles
of the speed reducers mean that foot-rests, sometimes even the user’s feet,
come into contact with the road surface during the exit. There is a risk that
small wheels may get stuck in the reflector housings in speed reducer 3.
Regarding all these observations, wheelchair users should have the possibility
to by-pass the speed reducers.
13
PUBLIC TRANSPORT
Two buses from the Transports en Commun de l’Agglomération Rouennaise
(TCAR) fleet were used to check if the speed reducers could be easily
mounted. The 2 vehicles used were a standard bus and a low-floor bus
“Crossway”.
The standard bus crossed all 3 speed reducers without difficulty.
The second vehicle bumped heavily on speed reducers 1 and 2 during the exit
phase. Buses of this type differ from other vehicles by their soft suspensions,
meaning that they have high-amplitude vertical body movement. The gearbox
casing gouged a mark approximately 2-cm deep in the speed reducer when
exiting, even though drivers crossed the speed reducers at very low speeds
(approximately 5 km/h).
Figure 8: a standard bus passing over speed reducer 1
Before any installation, a dialogue should be engaged between bus transport
authorities and road managers to ensure that speed reducers can be mounted
by buses without damages.
CONCLUSIONS
The creation of pedestrian-priority zones and their associated installations
made it necessary to examine cases where road managers were keen to build
speed reducers, and to consider the geometric properties that such speed
reducers might have.
The analysis carried out in this study identified definitions for the conditions
that a speed reducer would require to be installed in a pedestrian-priority
zone, i.e.:
- compel drivers of motor vehicles to speeds under 20 km/h;
14
-
be safe to cross for users of all types (light vehicles, powered twowheelers, bicycles, wheelchair users) or be by-passed;
not be considered too uncomfortable by users as a whole.
Testing performed on a private roads (not opened to general traffic) intended
to evaluate the 3 abovementioned conditions were carried out on 3 speed
reducer profiles selected from a literature review.
The table below presents a compilation of the results.
Average speed
V85
Maximum speed
Speed reducer 1
flat top hump
Speed reducer 2
Round top hump
Speed reducer 3
Short bump
Light vehicle
14 km/h
13 km/h
13 km/h
PTW
26 km/h
26 km/h
19 km/h
Light vehicle
18 km/h
16 km/h
16 km/h
PTW
31 km/h
32 km/h
26 km/h
Light vehicle
21 km/h
19 km/h
24 km/h
PTW
60 km/h
68 km/h
49 km/h
YES
YES
Light vehicle
PTW
Crossing ability
(all users)
YES
NO
Bicycle
Wheelchair
NO
NO
YES
Bus
PTW
NO by 100%
NO by 100%
NO by 53%
Bicycle
NO by 100%
NO by 100%
NO by 71%
PTW
NO by 80%
NO by 80%
YES by 73%
Bicycle
NO by 86%
NO by 100%
YES by 75%
Wheelchair
YES
YES
YES
Light vehicle
comfortable 57%
comfortable 50%
comfortable 25%
PTW
comfortable 56%
comfortable 71%
comfortable 14%
Bicycle
comfortable 56%
comfortable 89%
comfortable 22%
Sensation of slippery
surface
Sensation of
dangerousness
Impression of comfort
Key
Meets the required conditions
Fails to meet the required conditions
Concerning crossing speed, the results show that the average speed is under
20 km/h for all the speed reducers for light vehicles. It should be noted that
results of the comparison between speed and impression of discomfort show
that there is a risk that drivers of light vehicles could steadily increase crossing
speeds over speed reducer 3 as they become accustomed to it.
The results for powered two-wheelers show that a large majority of riders
cross all 3 types of speed reducer tested at speeds greater than 20 km/h.
Riders reduce their speeds slightly with speed reducer 3, although not enough
to meet the target. This is a result that would appear to be strongly correlated
to the type of powered two-wheeler: certain types, off-road trial bikes for
example, cross any type of speed reducer with ease. This means that
focusing on speed reducer geometry alone is not enough to both reduce the
15
speed of powered two-wheelers and ensure that the speed reducers remain
easy to cross by other types of vehicle.
From the safety standpoint, it appears that speed reducers 1 and 2 meet the
requirements, whereas passage over speed reducer 3 poses problems for
bicycles and powered two-wheelers. A majority of riders felt it to be
dangerous.
Speed reducers 1 and 2 are felt by most users to be comfortable, whatever
the transport mode, whereas speed reducer 3 is rated as uncomfortable.
These results are particularly measured amongst cyclists, thus the
implementation of a too uncomfortable speed reducer is not appropriate within
a zone partly dedicated to their needs.
Regarding buses, the bumping noted during passages over speed reducers 1
and 2 indicates that road managers and transport authorities must meet
together to ensure that buses used on these particular routes are able to pass
over any speed reducers without damages.
Trials performed with wheelchair users demonstrate that all the speed
reducers are extremely restrictive for them: speed reducers 1 and 2 are
difficult to cross whereas speed reducer 3 is unmountable. There is also a real
safety risk caused by the possibility of wheelchairs toppling over. Thus it is
necessary to design a by-pass of these speed reducers for people with
restricted mobility.
In conclusion, speed reducers 1 and 2 appear to be the only types that meet
the requirements, with the exception of the crossing speed of powered twowheelers. However, these trials focused on geometry and no study was
carried out on the possible impact of the installation methods (vertical or
horizontal signing, suitable road surface, etc.), or the influence of the
environment where the speed reducers are used. Taking these two elements
into account would probably lead to different speed variations. For real-world
situations, speed reducers 1 and 2 would be better suited as long as the
installation conditions are properly defined.
From a scientific standpoint, we conclude that:
- the discomfort threshold of 5 m/s², referred to in the literature as a level
that users will naturally seek not to exceed, is generally proved to be
accurate in our trials;
- Defining discomfort with only the vertical acceleration could be done
only at low speeds, and it’s inappropriate with certain types of speed
reducer, such as the small bump.
In the future, further research is needed into:
- how to define the implementation conditions of the speed reducers;
- the evaluation of these speed reducer in the real world and over an
extended period (to check how drivers get used to them);
- how to define physical parameters other than vertical acceleration that
must be taken into account when characterising discomfort felt by
users when crossing a speed reducer.
16
BIBLIOGRAPHY
- Ardeh, H.A., Shariatpanahi, M., Barhami, M.N. (2008) Multi-objective shape
optimization of speed humps, Iran.
- Bjarnason, S. (2004) Round top and flat top humps: the influence of design
on the effects, Lund Institute of Technology, Sweden.
- Dispositifs de ralentissement de la vitesse (1997), Centre de Recherches
Routières Belge, Bulletin trimestriel du Centre de Recherches Routières
Belge, Belgium.
- Guide des ralentisseurs de type dos d'âne et trapézoïdal (1994), CERTU,
France.
- Claude, F. (2007) Étude de la relation entre la vitesse et le confort du
conducteur d'un tracteur agricole lors du franchissement de dispositifs
surélevés, Faculté universitaire des sciences agronomiques de Gembloux,
Belgium.
- Jehaes, S. (1998), Ralentisseurs de vitesse et plateaux: efficaces et
confortables ? Centre de Recherches Routières belge, Belgium.
- Les caractéristiques et conditions de réalisations des ralentisseurs de type
trapézoïdal, décret 94-447 du 27 mai 1994, Journal Officiel, France.
- Les caractéristiques géométriques, les règles de réalisation et de visibilité
des ralentisseurs de type dos d'âne ou de type trapézoïdal (1994), norme NFP 98-300, AFNOR, France.
- Mohammadipour, A.H. (2008), The optimization of the geometric crosssection dimensions of raised pedestrian crosswalks, Qazvin Islamic Azad
University, Iran.
- Ralentisseurs, vous avez dit dos d'âne! (1992), SETRA, France
- Watts, G.R., Harris, G.J. (1973) Road humps for the control of vehicle
speeds, Transport Road Research Laboratory Report, UK.
- Weber, A., Braaksma, P. (2000) Towards a North American Geometric
Design Standard for Speed Humps, ITE Journal, Canada.
- Zaidel, D., Hakkert, A.S., Pistiner, A.H. (1992) The use of road humps for
moderating speeds on urban streets, Accident analysis and prevention, Vol.
24, N° 1, pp 45-56.
17

EXPERIMENTATION OF NEW SPEED REDUCER PROFILES

Transcription

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