Chennai to Mahabalipuram distance is about 50km (31miles). It is about 1 hour plus drive by road. You can take either of the two roads, the OMR (Old Mahabalipuram Road) or the ECR (East Coast Road / State Highway 49) to reach Mahabalipuram. The ECR as the name suggests runs along the coast. The travel distance for both the routes are comparable, the OMR route is a bit longer. The ECR is a toll road and preferred route between the two to reach Mahabalipuram. Both ECR and OMR roads proceed to Pondicherry which is about 100km (62miles) south of Mahabalipuram.
A milestone in Tamil language on the ECR showing distances to Pondicherry (101 km) and Mahabalipuram (5km)
The ECR , that connects Mahabalipuram with Chennai and Pondicherry .