How to Get There from chennai
By Bus
You can get one of the many buses to Pondicherry at the main bus station at Koyambedu. Most of these buses are quite inexpensive and offer very basic facilities and lack both air-conditioning and comfortable seating. The buses get rather packed with a lot more people than are supposed to be permitted on board and is definitely not the recommended choice. The journey takes between three and four hours, depending upon what kind of bus you take.
By Road
The preferred road from Chennai to Pondicherry is the East Coast Road (commonly knows as ECR). This is a very scenic highway, with sand dunes on one side of the road and the sea on the other. The journey takes about two to three hours. Midway you cross Mahabalipuram which has a number of temples you could visit. There are also a few resorts where you can stop to dine. This route passes through Mahabalipuram, Kalpakkam, Marakkanam, and Kalapet before reaching Pondicherry.
The other road to Pondicherry is the National Highway 45 (NH-45), also known as the Grand Southern Trunk or the GST Road. Taking this road will take you about 3.5 hours to reach Pondy. This road is less scenic but a lot safer than the ECR as it has a divider between both sides of the road for much of the way. This road passes through Tambaram, Chengelpet, Madhurantakam, Melmaruvathur, and Tindivanam before reaching Pondicherry.
Many taxi services are available on this route. Taking a taxi from Pondicherry works out a lot cheaper than hiring one from Chennai. However, as you have to pay for a return trip for the taxi this might not always be true. Make sure that your driver drives within the speed limit of 60-80 kms/hour.
For the folk who want to drive down, both of these roads offer a great experience. There isn't too much traffic, the roads are of good quality. You just have to make sure you don't get too excited and hit the accelerator. Drive with caution, especially on the ECR, as a number of accidents have occurred on that road.
By Train
There is a train that leaves Pondicherry railway station at 5:30 AM daily and reaches Egmore Station in the Chennai at 9 AM. It returns from Chennai to Pondicherry at 6 PM and reaches at around 9:30 PM. It's not the most luxurious of trains and tends to get a bit crowded. Tickets are usually available at the railway station counter.