Overview
Traffic and transport continue to be the key economic factors. According to a study performed by the official German Automobile Club (ADAC), traffic jams at German 'Autobahns' are mostly attributable to accidents (33%), road construction (31%), and inadequate capacity/excess demand (32%). The resulting losses to economy have been estimated at about 250 million Euros per day. The cluster project is part of the research initiative INVENT.
The objective is to enable a smoother flow of traffic with fewer incidents and disturbances and consequently lower economic costs. Every participant in traffic will benefit, since better traffic flow means shorter trip times, better gas mileage, reduced emissions, as well as decreased driving stress and increased traffic safety.
Focussing on highways, the project will distinguish three critical areas of application:
- maintaining high flows in merging sections;
- preventing transitions to stop-and-go traffic;
- accelerating recovery from jams (congestion dissipation).
Investigations in previous projects such as Sandy or MoTiV have shown that in many traffic situations, the traffic volume (flow rate, or rate at which vehicles pass a point) actually attained is lower than the volume that could be carried under favourable conditions. A familiar example is the limited flow rate at the downstream end of a traffic jam amounting to only about 1800 vehicles per hour (per lane), i.e., about one vehicle every two seconds. This flow rate is about one third lower than the maximum attainable traffic volume in free, undisturbed flow. As long as this limitation holds, it is impossible for a traffic jam to dissipate at 1800 to 2000 vehicles per hour.There are just two distinct approaches one can take to dissipate jams, either raise the outflow or reduce the inflow. A combination of these two strategies appears particularly promising.
Reduction of inflow into the jam can be achieved in several ways:
- One possibility is diversion of vehicles onto an alternate route. This of course requires detailed information not only for the original congestion, but also for the alternate route, in order to be certain that the recommended detour indeed represents the better alternative.
- A second possibility is to reduce the mean vehicle speed in the region upstream of the jam.
- A third method is known as ramp metering, which is already practiced in various countries. Comparing vehicles leaving a traffic jam with vehicles starting from rest when a typical city traffic light turns green, one observes significantly shorter reaction times at the green light and consequently higher flow rates. The change from red to green is a signal that prepares the driver to accelerate to normal speed to start. If drivers leaving a jam were to receive a similar signal, this could shorten their reaction times, accelerate recovery to normal speed, and thus enable a higher outflow from the jam. Implementation of this strategy requires precise localization of the downstream jam end in space and time.
Based on this information, accelerated jam dissipation could be implemented in three stages:
- First by simply providing the information to drivers;
- Second by providing explicit verbal or visual driving recommendations; and
- Finally by using autonomously acting driving assistance systems.
In order to implement the strategies on a section of highway, detailed information co