The Jarlsberg Tunnel runs roughly north-south through Frodeåsen, a hill just north of the town center of Tønsberg. The northern entrance is located at Tomsbakken, beside County Road 35 and the southern entrance is located at Frodegata in the town center. Just south of the tunnel lies Tønsberg Station. The tunnel is long, of which is blasted through bedrock and is concrete culvert. The portal on the Tønsberg side is long.