You can put this tool to work in two different situations. One is in the corners of the intersection between two highways. Poke your on-ramp tool snug in the corner there, and if the tiles turn blue you�re all set to build an interchange. That is, if you�ve been taking care of business and have enough money in the treasury.

The other situation is where a road crosses under a highway. You can�t put a ramp on just any stretch of highway. There has to be a road to drive on from, or off to -- otherwise some poor sap of a Sim would drive off the highway into nothing, and the transportation department would have to send out a crew to clean up the mess.

The main trick is to point your On-ramp tool a tile or two to the side of the road, right next to the highway. Once again, if it turns blue you�re in business. If it stays red, there are a couple of things to look for. One is uneven terrain. Though the construction crews can make highways go over all sorts of bumpy terrain, for an on-ramp they need at least three flat tiles, at the same elevation as the highway, counting from the spot where the road and the highway intersect. Oh, and if there�s anything built on one of those tiles -- a park, say, or a zone with something already built on it? Uh-uh.