The street circuit course measured 52.15 miles long from the start-line at the Quarterbridge area in the town of Douglas. The circuit was based on a number of public roads including:
The highest point of the course was at Brandywell on the primary A18 Mountain Road measuring a spot height of 422 metres (1,384 feet) above sea level. 54°14′47.47″N 4°27′57.18″W / 54.2465194°N 4.4658833°W / 54.2465194; -4.4658833
For the 1906 Tourist Trophy Race the Highroad course was amended to a distance of 40.38 miles to prevent disruption to railway services. The start was moved from Quarterbridge to the road junction of the A2 Quarterbridge Road/Alexander Drive adjacent to the property called 'Woodlands' in the town of Douglas. Again the course was based on a number of public roads closed for racing:
Motor racing began on the Isle of Man in 1904 with the Gordon Bennett Trial and was originally restricted to touring automobiles. As the Motor Car Act 1903 placed a speed restriction of 20 mph on automobiles in the United Kingdom, the Secretary of the Automobile Car Club of Britain and Ireland approached the authorities in the Isle of Man for the permission to race automobiles on public roads.2 The act approved by Tynwald, the Highways (Light Locomotive) Act 1904, gave permission for the 52.15 mile Highroads Course for the 1904 Gordon Bennett Car Trial.
54°10′18″N 4°29′31″W / 54.17167°N 4.49194°W / 54.17167; -4.49194
TT Pioneers – Early Car Racing in the Isle of Man pp 22 Robert Kelly, Mercury Asset Management (1996)(1st Edition) The Manx Experience, The Alden Press ISBN No 1 873120 61 3 ↩
Island Racer 2004 pp 112–113 Mortons Media Group Ltd ISSN 1743-5838 ↩