A Várhelyi | PubMed Health

PubMed2000

The effects on safety, time consumption and environment of large scale use of roundabouts in an urban area: a case study.

An experiment with small roundabouts-as speed reducing measures-was carried out in a Swedish city. The purpose of the study was to test the large scale and long term effects of the roundabouts. The results showed that the roundabouts reduced the speed considerably at the junctions and on links between roundabouts. The lateral displacement the roundabout forces the driver to has a great importance for the speed of approaching cars to a roundabout. The speed-reducing effect is large already at a 2 m deflection. A larger deflection does not result in a larger effect. Conflict studies indicated an overall decrease in accident risk by 44%. Vulnerable road-users' risk was reduced significantly, while there was no reduction for car occupants. There is a relation between the reduction of approach speed and the reduction of injury accident risk. The time consumption at a time operated signal was reduced heavily by the instalment of a roundabout at a signalised intersection. On average, emissions (CO and NOx) at roundabouts replacing non-signalised junctions increased by between 4 and 6%, while a roundabout replacing a signalised intersection led to a reduction by between 20 and 29%. The noise level was reduced at junctions that were provided with roundabout. Car drivers were less positive to the roundabouts than bicyclists. In the long term, the unchanged roundabouts worked almost as good as they did shortly after the rebuilding. The study showed that details in the design are of decisive importance for road-users' safety. Special attention has to be paid to the situation of bicyclists. The transition between the cycle path/lane and the junction has to be designed with care-the bicyclists should be integrated with motorised traffic before they enter the roundabout. There should be only one car lane both on the approach, in the circulating area and on the exit. The size of the roundabout shall be as small as possible.

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PubMed1998

Drivers' speed behaviour at a zebra crossing: a case study.

The purpose of the study was to: (1) observe the frequency of giving way to pedestrians at the zebra crossing; (2) reveal speed adaptation problems; (3) examine if the time difference between the arrival of the pedestrian and the car have any influence on the speed of the approaching car; (4) identify so-called 'ideal' situations (in which the car brakes on the driver's own initiative in order to give way to a pedestrian) upon which recommendations can be given for implementing means to improve speed behaviour at zebra crossings. It was hypothesized that the speed behaviour of drivers approaching the zebra crossing depends on the pedestrian's arrival at the curb related to the car's expected arrival at the zebra crossing. The speed was measured on randomly selected 'free' passenger cars which approached a non-signalized mid-block zebra crossing on a two-lane arterial road. Every second a radar gun, hidden at the road side, sent the speed data to a lap-top computer in which the observer could also register pedestrians' arrival at, and start from the curb. Simultaneous video recordings were made in order to obtain a more detailed description of the interaction between the car and the pedestrian. Speed behaviour in encounters (148 observations), non-encounters with pedestrian presence (642 observations) and situations without pedestrian presence (690 observations) was compared. Situations with pedestrian priority were classified. The results show that the frequency of giving way is 5%. Drivers do not observe the law concerning speed behaviour at the zebra crossing, as they do not "adapt the speed in such way that they do not endanger pedestrians who are already on, or are about to step onto the zebra crossing". In encounters, three out of four drivers maintain the same speed or accelerate and only one out of four slows down or brakes. These results indicate that maintained high speed (even exceeding the speed limit of 50 km hour-1) is the signal from the drivers that they do not intend to give way to the pedestrian at the zebra crossing. The conclusion is that encounters between cars and pedestrians at the zebra crossing are critical situations in which the driver has to be influenced before he reaches the decision zone at 50 to 40 m before the zebra crossing in order to prevent the 'signalling by speed' behaviour. Countermeasures to improve driver behaviour at the zebra crossing are discussed.

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