Thank you for playing, I'm glad you liked it :)
Having more vehicle weight variety and speeds will be hell to balance the levels, you see I made sure every level can be completed (ignoring a bug on level 3) with the vehicles provided for it.
Having keyboard controls is an absolute great idea, I didn't think of that but it makes perfect sense. It gives more control of when you spawn vehicles and could challenge players to have more vehicles on the bridge at the same time and also beat the level faster (like a speedrun I guess).
Thank you for your feedback, it is greatly appreciated! :)