Regional Jet 900 (CRJ900)
Flight Crew Air Transport Pilot (ATP)
Confusion; Situational Awareness
Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Human Factors; Airport; Procedure
It had just become nighttime. Detroit uses Runway 9L as a taxiway. We were taxiing on 9L with the pre-takeoff briefing complete. Instructed to exit left on Taxiway M on our way to depart 21R. The Captain said something to the effect of 'I need to make sure not to miss Mike.' Just then I looked to the left and saw we were passing Mike. I said 'Stop.' We MIGHT have been able to slam on the brakes at that time and make a 110 degree turn onto Mike; but instead the Captain brought the aircraft to a non-abrupt stop SHORT of active Runway 21R. I informed Ground that we had overshot Mike but were holding short of 21R. No aircraft was in the takeoff phase at that time. Ground directed [us] onto 21R to make a U turn; then right turn onto Mike to continue for uneventful takeoff on 21R. At NO TIME did we encroach on Runway 21R. The biggest threat would be non-standard markings. Runway 9L is being used as a taxiway yet there is no hold short line on 9L to notify the crew that the next intersection is a runway; NOT a taxiway. As I am not assigned a lot of DTW flying; I am not sure if there might be some hold short lighting that might not have been working at the time; but such markings and lighting would be an extra help to any crew. Be hyper-aware while taxing on 9L. On our next departure; we were assigned the same instructions. I asked for the easy taxi to 22L instead; which was granted. DTW was not terribly busy either time.
First Officer describes using Runway 9L as a taxiway at DTW and missing the left turn on to Mike as cleared. The next intersection is Runway 21R which the crew stops short of although there is no hold short line or signs.