I used to study traffic a lot, and it's definitely true that eating additional capacity leads to more gridlock assuming the same type of driver. However, consi

I used to study traffic a lot, and it's definitely true that eating additional capacity leads to more gridlock assuming the same type of driver. However, consider the freeway case as a starting point. Freeways lock up because of congestion resulting from too many people merging on, causing people to plan poorly/brake suddenly, which leads to a recursive accordion effect, which leads to 5-10 mph stop and go for hours. However, the actual throughput of cars past any one point on the freeway is actually higher at around 40-50 mph (you should get 1.5 - 2x throughput that you get at 10mph), assuming everyone is organized enough[1]. Now imagine pace cars whose sole job it is is to buffer and reduce the negative impacts of poor human decision on the freeway, with a total car increase of only 1-5%. [1] Sorry, I don't remember the source, but I swear I had one a few years ago when I was heavy into traffic.