ELI5 Traffic Lights - why not use pressure sensors?

How intelligent are traffic light systems? What sensors are used? Why not use pressure sensors under the pavement? How do traffic systems coordinate across intersections in a city? Do emergency services like fire trucks and ambulances have the ability to control traffic signals? ... we explain like I'm five Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: anthonypalumbo, blipsman, powerclean, nagisan and bigredinmass. To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Join us on Twitter: https://www.twitter.com/eli5ThePodcast/ or send us an e-mail: [e-mail]