Most transportation options are unable to handle peak demand during rush hour in order to keep congestion down.
Congestion occurs when the maximum road capacity is reached, sharply decreasing the speed (e.g. 55mph to 15mph on Madrid’s M-30) and capacity to admit new vehicles. Even when the number of vehicles drops, the unsatisfied demand creates congested traffic. Congestion results in 3-4 higher travel times and higher pollution, given that each car caught in congestion emits 80% more emissions.
The only solution is to decrease the number of vehicles below the road’s saturation level. A million cars in Madrid, where four out of five cars carry just a single driver, means there’s a waste off four million empty seats even during rush hour. This is more than the people traveling by metro or bus. In a best-case scenario where those four million seats would be utilized, then the number of cars would be four times lower. However, as the graph below showcases, just a relatively low number of cars shared would keep the number of vehicles below the saturation level and avoid congestion.
A study from MIT shows that 98% of New York City's taxi demand can be covered with just 3,000 four-passenger vehicles (14,000 taxis currently operate in the city) with an average wait time of only 2.7 minutes . Only 2,000 10-passanger vans would also have a similar effect. The MIT model allows to evaluates the trade-offs between fleet size, capacity, waiting time, travel delay, and operational costs for a range of vehicles.
The system MIT proposes works by graphing all possible trip combinations of the trip requests and available vehicles, and then uses “integer linear programming” to compute the best assignment of vehicles to trips. The model can then rebalance the remaining idle vehicles by sending them to higher-demand areas.
In reference to the above, instead of congestion charges cities should more actively look into promoting and even subsidizing ride-sharing.
Written by Magda Collado, RISE Viktoria.
2. 2016-12-01. Study: carpooling apps could reduce taxi traffic 75