You can hit vehicle limit on any size map. I would check warehouses first as they seem to have issues right now. Then look to your traffic flow %, higher is always better. Massive bike traffic can cause issues, each bike is a vehicle. Get cims on mass transit instead. Reevaluate your Mass Transit. One super bendy bus is really 3 buses running as one. 10 =30 buses. Go through all your Mass Transit adjust as necessary. If you would like help, post more information as it will be needed. City population, traffic flow, imports/exports. Screen shots are helpful to so others can see what's happening.
As Mayor and City Planner of your city you need to plan and make adjustments as necessary. It is a game with limits, there is information on line on the limits and suggestions on how to cope with them. Or post and people will help with suggestions on improvements. Good luck.