Once both efforts are realized, there will be so many trains traveling through the corridor that in downtown San Mateo, cars could be stuck at railroad crossings for as long as 20 minutes per peak hour, said Brad Underwood, San Mateo’s Public Works director.  And that’s based on Caltrain’s “baseline” growth scenario. If Caltrain opts for the “high-growth” scenario then gate downtime goes up to almost 27 minutes per peak hour.

“It’s a huge concern in the city,” Underwood said.  San Mateo councilmembers have echoed the concern.  “We can’t have our intersections closed for 26 minutes during peak hours. It shuts down the city,” Councilwoman Diane Papan said at a meeting in August.

Back in 2015, the frequency of trains was well-documented, for example in Part 108 of this saga 

Parsons said the high-speed rail system could carry 116 million passengers a year, based on running trains with 1,000 seats both north and south every five minutes, 19 hours a day and 365 days a year. The study assumes the trains would be 70% full on average.

It was old news five years ago, but San Mateo is just waking up to the problem.  Years ago San Mateo was a non-player in the Peninsula Cities Consortium that sought to stop high-speed rail's destruction of the Peninsula and our collective budgets.  Now their residents will have to sit in their electric vehicles pondering the waste of time, money and reduced emergency vehicle response time because of that decision.