From the "Getting Around" section of the Rough Guide

The Gambia has no railway lines, and no internal flights except by private arrangement. The most common way to get around is by road, which is often a slow, dusty and bumpy experience. Travel is severely hampered by the state of the country’s roads. The major artery which runs all the way along the south bank of the River Gambia from Banjul to Basse, via Serrekunda, Brikama, and Soma, was sealed in the 1970s, then neglected so badly that a few stretches (most notoriously the 100km or so west of Soma) are currently a nightmarish mess of potholes. The photo on the left was taken on the north bank, a relatively smooth stretch of dust (or mud, in the rains) between Kerewan and Farafenni.

In many ways cycling is the ideal form of transport in The Gambia. It gives you total independence; you can camp or take your bike into hotel rooms with you. If you get tired of pedalling you can transport your bike on top of a bush taxi or bus (reckon on paying about half-fare for it). A bike allows you to explore well off the beaten track. Routes that can’t be used by motor vehicles because they’re too rough, or involve crossing creeks, are all accessible. With a tough bike, you can follow bush paths and if your tyres are up to it you can also ride along the beach at low tide (leaving the bumsters standing). You can rent bicycles from a number of bike rental stalls on the coast, mostly near major hotels. The quality varies hugely. The going rate is reasonable at around D200-300 (£4–6/€6-9 per day), with discounts negotiable for longer periods. These two Dutch cyclists on their way up to Tendaba camp, had cycled from Dakar, Senegal