Hi Peter,
The second option will probably look a little more realistic, it is rare to find a road running parallel to a tunnel mouth, even at Kemble there is a reasonable gap between the tunnel mouth and road:
http://maps.google.co.uk/maps?q=kemble&bav=on.2,or.r_qf.&bvm=bv.45645796,d.d2k&biw=1024&bih=651&wrapid=tlif136699786194310&um=1&ie=UTF-8&sa=X&ei=Ybt6UaH2L6nT0QXei4B4&ved=0CAgQ_AUoAg