Here's a rough system I've been working on.
The chaser and chasee's movement and manouvres are relative to each other, not the surrounding terrain. So allow whoever has initiative to say how difficult they want their action that round to be: DC 10+ a modifier that goes 2-4-8-16. The other party can then match that, or bid for a higher modifier. Apply modifiers as appropriate.
Example 1: If the PCs are escaping, but trying to act casual and blend in with the crowd, for example, they'll select a DC of 12. The baddies want to catch them, without causing too much havoc, so they select a DC of 14. If both succeed, it means that the baddies have caught up with the PCs (but not necessarily stopped them). If the baddies roll below 14, but at least 12, they still have a tail on the PCs. If they roll less than 12, the PCs have blended into the crowd and are off.
Example 2: If the baddies are escaping in a taxi in New York, and don't care about the chaos they cause, they choose a DC of 18. The PCs just want to keep them in sight, without causing any damage to the surroundings just yet, so they match the DC of 18. But they're driving a hop-on hop-off double decker bus, so they get a +2 bonus to keep sight of the baddies' taxi. If they want to overtake the baddies, they'd have to roll DC 26, with a -4 penalty because a large bus is less manouvrable. So if the baddies roll an 18 or better, the PCs need to roll 30 or more to overtake the baddies; if they roll 16-29 they keep them in sight, and if they roll 15 or less they lose them.
You can fill in the description of the case to match the rolls.