The road section is on the cpu board (top) but spans 3 pages in the schematics and is highly complex. It could be a bad PAL, TTL or RAM. Without special equipment (logic probe, oscilloscope, ability to burn new PALs or have good PALs handy) the only thing you can do is verify the contents of the road ROMs IC11 and IC47. If those are good I would suggest to send it to Ken at irepairsega.com he will sort it out.
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