US‑36 locals still ride AB1 from DEN to Boulder
RTD’s AB1 bus runs from Denver International Airport to Boulder via the old US‑36 corridor, serving stops like the US‑36 & Flatiron Station and several park‑and‑rides along the way. It boards at the RTD bus bays on Level 5, Jeppesen Terminal, island 5, usually in the “Regional/AB” area. The route is aimed at people who already live near those intermediate stops, not first‑time visitors trying to reach downtown Boulder from scratch.
Typical scheduled runtime sits around 1 hour 10 minutes from DEN to downtown Boulder Station, but riders on Reddit report it can stretch past that during US‑36 rush hour. Fares follow RTD’s regional pricing, so check the current regional fare before you go; you can pay with the RTD MyRide app or cash on board. The bus runs daily, but frequency drops outside commute hours and on weekends.
Morning and late‑night gaps matter here: several Boulder‑based travelers warn that AB1 and its sibling AB2 no longer run as often as they did a decade ago. One regular notes that the A Line train plus the Flatiron Flyer can beat AB1 on total time, especially in the middle of the day. If your flight departs before 7:00 a.m. or lands after 10:00 p.m., pull up the specific trip times, not just the generic frequency.
Luggage space exists but feels tight when a full airport crowd piles on with 62‑inch checked bags before Thanksgiving or Christmas. These are standard regional coaches, not dedicated airport shuttles with huge underfloor bays on every departure. Riders in r/denver threads suggest boarding at the airport origin stop rather than a mid‑route park‑and‑ride if you’re carrying more than one suitcase or traveling with ski gear.
Regulars in Boulder often default to the Flatiron Flyer plus A Line combo, especially outside AB1’s stronger morning and evening blocks. That means: Flatiron Flyer to Denver Union Station, then the A Line train straight to DEN in about 37 minutes from Union. They shift back to AB1 mainly when they live near specific US‑36 stops and the timetable lines up neatly with a mid‑day or early‑evening flight.
Quick step‑by‑step from DEN to Boulder on AB1:
- 1. After baggage claim on Level 5, walk outside Jeppesen Terminal to island 5 and look for the “Regional/AB” signage.
- 2. Check the electronic RTD board for the next AB1 departure time toward Boulder Station; aim to be there 10–15 minutes early.
- 3. Buy a regional fare on the RTD MyRide app or have exact cash ready (RTD does not give change).
- 4. Line up near the front door, load larger bags into the luggage rack immediately inside, and keep smaller items at your seat.
- 5. Get off at your park‑and‑ride or stay on to Boulder Station, then use local buses, B‑cycle, or a quick rideshare to reach your final address.
One tip: check the last‑bus time from DEN to Boulder the night before; miss it, and you may be looking at a $70–$100 rideshare instead.