This is helpful with drawing precise curves such as building custom roundabouts.
You can build bridges and tunnels by adjusting the road's elevation with Page Up and Page Down keys.The price is usually determined by the amount of tiles the road segment has and then the price for that segment when building gets divided by 2.) The refund value will gradually decrease to zero over time. (This is usually half of the original price. You can bulldoze the two lane road piece and get a partial refund. Building a short segment of two lane road anywhere within city limits unlocks more roads, such as a one way road which is useful with the highway stubs you're provided at the start.
