From 20th and Fox St.(Now the location of Coors Field) drive north on 20th over I-25. Next segment is unknown but he ends up on Colfax in the Capitol Hill area, where he buys some speed. Then he heads east on Colfax, south on Colorado Blvd. to I-25, and then back north to I-70 West.
The motorcycle cops chase scene is up around Georgetown, CO. Then he would have taken US 6 over Loveland Pass (the Eisenhauer/Johnson tunnels weren't finished yet), then on along the I-70/US 6 route over Vail pass to Glenwood Canyon. There is a chase scene through the canyon near No Name which then proceeds through Glenwood Springs and Rifle, the Debeque Canyon and through Grand Junction, (giving a nice pan shot of the Grand Mesa during his little West bound to East bound lane switches BTW). I lived in the Grand Junction area back in the early-mid '80's, and travelled the above route between Denver and G.J. probably 40 times or more.
The next segment of the journey is a little fuzzier. He stays on the interstate/ US 6 route through Thompson, but inexplicably travels south on US 191 towards Moab. As a side note, the town where the ending crash was filmed, Cisco, was there, near the Colorado/Utah border instead of California as depicted in the movie. Then Kowalski ends up on UT Rte 24 southwest of Green River, UT, another stretch of road I have travelled numerous times since I used to live at Lake Powell, and still visit there frequently since my brother is still living there. Then there's a few shots taken west of Hanksville, UT near the Capitol Reef area, where the one lane bridge in question used to be. One can only assume by this that his route would have taken him back up to the present day I-70, through Salina, and across on US 50 to Delta, UT and into Nevada. However, some scenes were shot north of here near Wendover, so perhaps he took UT-28 north from Salina and then cut across to UT-36 and up to I-80? Why he would have gone 100 miles out of his way just to double back only the director knows for sure. d;-)
From Wendover, you take Alt US-93 south to US-50, then across to Austin where you jump on NV Rte. 376 down to Tonopah. A Side trip to Goldfield is a must, to see the KOW radio station (Goldfield Hotel). Then back up to US-6 and west over to US-95. Somewhere between Hawthorn and Fallon (I believe it was in the vacinity of Walker Lake) he heads out into the desert and finds Dean Jagger, Bonnie & Delaney and the freaky Pentacostal snake charmer minister.
From there it's anybody's guess, since there's no Cisco, CA. I would assume that he wouldn't take US-50, and instead ended up on US-395 or NV-359 near Mono Lake. 359 would be my choice, since he was looking for a "back door" into California. Then perhaps north on 395 to the fictional Cisco, CA. I made this determination due to the positioning of place names on the CHP map board; ie. Stockton, Oakland, San Fran., etc. Hope this helps plan your next road trip!