His research spans three areas:
- Transit planning
- Traffic signal control
- Bicycle and pedestrian transportation, including safe street design
His transit research covers routing and scheduling, data collection, and passenger flow modeling.
He has been a consultant to more than 25 transit agencies nationwide.
In traffic signal control, Peter has been a leader in developing control techniques for transit signal priority and efficient adaptive control. His bicycling / pedestrian / safe streets design research has included bike facility design, bike safety, Vision Zero policy, intersection design, and bike network planning.
He is the inventor of the widely used Level of Traffic Stress method for evaluating bicycling networks, for which he received the Lifetime Achievement Award from the Association of Pedestrian and Bicycling Professionals.
In the summers, he teaches a 5-week course in the Netherlands on sustainable urban transportation, exposing American students to Dutch best practices in bikeway design, transit priority, transit- and bike-oriented urban planning, and traffic safety.