Experimentation of New Speed Reducer Profiles Suitable for Maximum Speeds of 20 Km/h
N Dubos, E Evian, CETE Normandie Centre, FR
Definition and assessment of new road hump profiles reducing crossing speeds under 20km/h
Quantitative and qualitative analysis of their influence on the users' behaviours, especially the vulnerable ones (pedestrians, cyclists and motorcyclists).
In France the concept of pedestrian priority zone opened to through traffic has been introduced in the regulation since july 2008. In these zones non-motorised users are given the right of way. They can cross the area at any time in front of a car or a motorcycle, walk in the center of the street. To ensure vulnerable users? safety the usual speed of a motorised user should be very low; therefore speed limit in this zone is set to a maximum of 20 km/h. The design of such areas should provide self explanatory behaviour for users. But it may happen in some places that road users would not drive as slow as needed. As a result some cities may lay road devices, such as road humps, across the streets to oblige drivers to travel at a speed lower than 20 km/h.
In order to avoid the proliferation of unsuitable speed reducing devices, the Centre d'Études Techniques de l'Équipement Normandie Centre (CETE NC), a regional technical service reporting to the French ministry of Transport, was asked to define and test road hump profiles adapted to a maximal speed of 20 km/h.
The experimental objective is to evaluate whether the road hump profiles selected from the results of a literature review, are run across at speeds lower than 20 km/h and safely traversable by all users, including wheelchair users. Also the literature review shows that some road humps are more comfortable in higher crossing speed than in lower speed. Such parameter had to be evaluated for the selected profiles.
The following criteria are then measured:
- Crossing speed by powered users.
- Driver behaviour differences according to different types of vehicles.
- Traversability and safety of any road hump.
- Road hump performances (relationship between crossing speed and vertical acceleration).
- Comfort during crossing.
The selected road humps are:
- Road hump #1: a flat top hump with a total length of 3m and height of 10cm with a plateau of 2m.
- Road hump #2: a round top hump with a total length of 2m and height of 10cm.
- Road hump #3: a short round top bump of 0,5m length and height of 7cm.
These three different road humps were built in CETE?s precinct, closed to any traffic, in mid-2009.
The experiment has been focused only on the geometrical characteristics of the road humps. The installation conditions haven?t been treated and they have to be defined: what kind of horizontal road marking or vertical signing, type of surfacing, best implantation in the shared space, etc
Tests consisted in driving different cars or road users across the three road humps in order to look at drivers? behaviours, measure their speeds and interview them to know what they think about them. Moreover, physical parameters such as speed or vertical acceleration were recorded with an instrumented car during the experimentation.
A panel of various road users went through the road humps: cars, motorcycles or bicycles. To be representative, numerous drivers were recruited among regional representative associations and volunteers among CETE?s staff. All the subjects accepted to use their own vehicles to cross the tested road humps.
The experimental results show that:
- The three tested road humps are overall efficient for cars to reduce speed under 20 km/h but they?re not efficient for motorcycles.
- For road humps #1 and #2 the maximal vertical acceleration is a linear function with crossing speed under 20 km/h and it becomes a constant value from 20 to 40 km/h.
- For road hump #3, the maximal vertical acceleration is a linear function with crossing speed at any speed.
- A vertical acceleration value of 5 m/s², the usual threshold of discomfort found in the literature review, is reached at a crossing speed of 15 km/h for road humps #1 and #2. For the road hump #3, values are over the threshold at low speeds.
- Vertical acceleration isn?t the only parameter to be considered in order to qualify discomfort inside some speed interval or for short road hump.
This study will go on throughout 2010 to evaluate the performance of a long flat top plateau with subjects including disabled people (persons with restricted mobility). Moreover the installation conditions have to be defined, new tests on a real-world urban site have to be carried out.
Association for European Transport