Why are the buses not on time?

It is well known: the press never talks about trains that arrive on schedule. Neither do people. If, on the whole, Swiss public transportation networks are as reliable as Swiss watches, they regularly take some flak, especially for delays during rush hour and on certain more sensitive routes. And when one bus steps out of beat, it can have repercussions throughout the network. A group of second-year civil engineering students recently evaluated data provided by the Fribourg Public Transportation Services (TPF) from several bus lines, looking for flaws, their causes, and to propose solutions.

The researchers based themselves on two sources of data: the bus schedules that are set by the TPF, and real-life observations made using an onboard GPS system. Distances between stops were measured using Google Earth. Under the supervision of Nan Zheng from the Laboratory of Urban Transportation Systems, Hadi Karam, Benjamin Schaer, and Levy Sharabi combined these data with spatial data for the two bus lines that were causing most problems.

By analyzing the data they were able to identify exactly which route segments and bus stops triggered the delays, which were exacerbated during peak traffic hours. It also helped them determine their causes. For example, on one of the lines during rush hour traffic, the buses regularly fall a few minutes behind schedule between two stops. Along that more than one kilometer long segment, the bus only has a priority bus lane for half the distance. It then crosses a roundabout, where it has to yield to countless other vehicles. And because this bottleneck is at the beginning of the line, the delay it causes persists throughout the entire journey.

Intentional delays
At each bottleneck, the researchers sought to find the root causes of the delays – an incomplete bus lane, a too busy street, a roundabout saturated by a busy tributary, the lack of dedicated traffic lights, or a segment on a key artery in the city center. They were also able to show that the time spent at bus stops has little influence on delays and is not worth acting on.

The first solution the researchers proposed is based on the satisfying demand: “Given that there is a delay, how can it be used to serve the passengers?” In other words, on bus lines that are serviced at a low frequency, about every 10 to 15 minutes, buses that are so severely delayed that they would service a stop a few minutes before the next bus is scheduled could simply add a few minutes to their delay and take up the next bus’s slot. Such so-called intentional delay would allow passengers arriving at the bus stop on time to catch a bus, rather than forcing them to wait another 10 to 15 minutes. However, to avoid overloading the buses, the delayed bus should not be made to wait for more than two to three minutes in order to take over the next bus’s scheduled departure time.
Another, structural approach would involve setting up detectors and traffic lights that favor public transport services in the case of traffic jams. Rerouting bus lines and adding longer waiting times at the terminal stations as a buffer are other proposed measures. This project, coordinated by the Transportation Center, is a first step in an expanded collaboration with the TPF.