Carlos Daganzo

Carlos Daganzo is a traffic engineer whose work makes the dynamics of congestion concrete: a single vehicle moving substantially slower than surrounding traffic can disturb the flow across a highway. His research also informs a proposed approach to congestion pricing that would preserve incentives to avoid peak-time driving without letting drivers who can readily pay dominate the roads.

Identity and Research

Daganzo is identified as a traffic engineer associated with the Institute of Transportation Studies at Berkeley. The book presents him through two connected concerns: how bottlenecks disrupt traffic, and how road-use prices might manage congestion without making access depend simply on who can afford to buy time.

Congestion Pricing and Fairness

Daganzo proposed allowing people to drive for free on some days and charging them on others. The arrangement was offered as an alternative within the broader problem of designing congestion pricing: tolls can encourage drivers to change when or whether they travel, but a system must also account for unequal ability to trade money for convenience. In contrast to Mexico City’s license-plate restrictions, which left drivers free to use their cars on most days and encouraged some to buy second cars, pricing aims to preserve an incentive to seek alternatives. Daganzo’s proposal would retain that incentive while preventing those willing and able to pay from monopolizing highway capacity.

The Richmond–San Rafael Bridge Experiment

On the morning of June 14, 2000, Daganzo and fellow engineer Juan Munoz sent a test vehicle onto the Richmond–San Rafael Bridge near San Francisco. The five-and-a-half-mile bridge had two lanes in each direction and no entrance or exit ramps. Traffic was moving a little faster than sixty miles per hour, but the test vehicle was instructed to travel significantly more slowly than the prevailing flow.

The disturbance appeared immediately. Drivers changed lanes more often, and congestion began building farther back along the highway, or upstream. The bottleneck itself was moving rather than fixed, yet it still made a substantial dent in traffic flow. The demonstration showed how a relatively small difference in speed could act as an obstacle and impede traffic well beyond the vehicle that created it.

Why Bottlenecks Spread

Daganzo’s experiment illustrates the cascading effects of uneven lane speeds. When one lane moves more slowly than another, drivers are more likely to change lanes. Those changes make drivers cautious, leading them to leave larger gaps between vehicles; the extra space, paradoxically, can make further lane changes more likely. The result is reduced capacity: each lane carries about ten percent fewer vehicles than it would as a single-lane road.

As roads grow crowded, coordination becomes harder. Drivers have only brake lights and turn signals to communicate, and those limited signals can turn anticipation into overreaction. A driver who brakes too readily can slow an entire highway, while individual choices about changing lanes or leaving at an exit are made without a wider view of traffic. Against the patterned movement of a flock of birds, the resulting traffic jam is disorganized stop-and-go motion.