You can easily join the A14 from the M1 (J19 northbound) and the M1/M6 turnoff (J19 southbound).
From the town, follow the A6003 to A14 Cambridge/Peterborough, then straight over A14 (J10) and take the Burton Latimer turn off (3rd Exit).
Then second exit at roundabout towards the Morrison's Warehouse, and second exit at the Morrision's roundabout onto Polwell Lane.
The M1 is 15 - 20 minutes from the stadium.
Latimer Park has matchday parking on site but does hold a limited number of spaces.
There are regulations for on-street parking which are covered by the 31st March 2008, Traffic Management (TMA) Act for all non-residents, and please be aware that Penalty Charge Notices could be issued to all drivers who ignore the regulations.