Amsterdam experiment in mixing pedestrians, trams and bicycles, The

Institute of Transportation Engineers. ITE Journal, Aug 1999 by Zacharias, John

MIXED-MODE STREETS ARE BEING PROPOSED AS A SOLUTION TO LOCAL TRAFFIC AND LAND-USE PROBLEMS. IN THE STUDY DESCRIBED IN THIS FEATURE, A DE FACTO MIXED-MODE STREET IN AMSTERDAM WITH RELATIVELY HIGH TRAFFIC VOLUME WAS STUDIED TO DETERMINE HOW THE MODES AND DIRECTIONS ARE ACCOMMODATED.

PEDESTRIAN ZONES HAVE become a familiar feature in the central areas of European cities. Private cars are always excluded from these zones, while delivery vehicles are permitted during off-peak hours. Bicycles and taxis are typically relegated to a circumferential service road. Some have argued that such rigid traffic separation contributes to economic and environmental disparity between the pedestrian zone and its surroundings. The concentration of high-value retailing, services and pedestrians within the zone contrasts with low values and heavy car traffic at the periphery. Traffic-calming experiments during the 1970s and 1980s demonstrated that environmental design could reduce both the volume and the environmental impact of cars in local areas. These results have led to speculation about how a controlled mix of traffic modes might be made to lessen these central-area contrasts. The role of the bicycle in particular has not been addressed in pedestrian zone planning. The bicycle is typically treated as a vehicle even in those cities where its use is encouraged. However, since environmental design cannot be used to exclude cyclists from pedestrian areas, planners have to rely on cyclist adherence to regulation, a dubious proposition in many cities.

The Netherlands has consistently embraced the principles of traffic separation while promoting use of the bicycle. Pedestrianized core areas and an extensive system of separate bikeways are found in all major towns and cities. Bicycles are routinely used for all kinds of intra-urban trips and are found not only on bicycle pathways but on all other streets as well. The extensive pedestrian zones, some exceeding a 30-minute walk across the diameter, make the bicycle more attractive than pedestrian or public transportation alternatives. The bicycle offers significant time saving, relative safety and convenience.l The pedestrian zones provide cyclists with alternate routes that are often illegal but are nevertheless used on a regular basis. Authorities tolerate cyclist use of these pedestrian paths, as long as it does not contribute to pedestrian discomfort or accidents. Some Dutch observers argue that such a liberal approach works best since the level of cyclist use is largely self-regulating. According to the selfregulation theory, cyclists take responsibility for collision avoidance and pedal through pedestrianized zones if pedestrian traffic volumes allow them to do so comfortably and safely.

This de facto mixing of modes merits study for several reasons. If such systems can be made to work safely and efficiently, they can solve many planning problems. The major issues in addition to level of service are comfort, convenience, safety and attractiveness.2 While engineers have generally supported traffic separation as safer than mixing, not all agree with this view, citing the persistent accident rates at intersections of pedestrian and bicycle pathways with vehicular routes.3 The self-regulating theory also requires empirical verification. In particular, we need to understand how pedestrian volume flow level impacts on bicycle volume flow.

Separated bicycle pathways take space on the street, usually the width of a traffic lane in each direction. In Amsterdam as in many other cities in Europe and North America, implementing such an arrangement with separated footpaths means a drastic reduction in the space allocated to vehicles, if not their elimination from the street.

One of the major questions raised by such designs are their carrying capacity and, in particular, the sustainability of the traffic mix when the total volume of traffic is increased.4,5 Also, in the event that the number of pedestrians remains stable while the number of bicycles increases, will there be more conflict situations? Alternatively, if the number of pedestrians increases, how will this affect the cyclist's experience and his/her decision to use this street?

Effective width of the street is less than the real one because pedestrians do not use all of it.6 The design factors in preference for a particular path trajectory need to be examined. It has been suggested that walkway capacity will be reduced when there is two-way movement and when this movement is uneven.7 This is because the secondary flow will be dispersed in and among those moving in the opposite direction. Even flows in opposite directions will tend to sort into separate streams but only at density levels somewhat greater than those in the Leidsestraat. In typical commercial streets, there is bound to be an uneven distribution of pedestrians in the observed streams, and the streams themselves may not be stable. While such conditions may be tolerable for pedestrians traveling at approximately the same speed and with considerable maneuverability, this may not be the case when cyclists are added to the mix.