In realistic urban environments, emergency response vehicles may encounter one-way streets and barriers such as rivers that impede rapid response. Formulas are developed for the associated increase in mean travel distance, using a model in which both the demands for service and the locations of the vehicle are uniformly distributed over the response area. Barriers of even moderate size are found to increase average travel distance less than 10 percent, and a system of one-way streets increases the average distance by two block lengths. However, in 6.2 percent of responses on a one-way street grid, the vehicle has to travel an extra six block lengths.
Larson, Richard C., Response of Emergency Units: The Effects of Barriers, Discrete Streets, and One-Way Streets. Santa Monica, CA: RAND Corporation, 1971. https://www.rand.org/pubs/reports/R0675.html.
Larson, Richard C., Response of Emergency Units: The Effects of Barriers, Discrete Streets, and One-Way Streets, Santa Monica, Calif.: RAND Corporation, R-675-HUD, 1971. As of October 07, 2021: https://www.rand.org/pubs/reports/R0675.html