The FasTrak Flex is a switchable transponder that lets California drivers claim carpool discounts on Express Lanes and state-owned toll bridges by sliding a three-position switch to match the number of people in the car. A standard FasTrak tag pays the full toll every time, no matter how many passengers you have. The Flex is the only version that can tell the tolling system you qualify for a carpool rate.1Bay Area FasTrak. Using Your FasTrak Flex Toll Tag FAQs
How the Three-Position Switch Works
The toggle on the front of the transponder has three settings: 1, 2, and 3+. Set it to match your occupancy before you reach the tolling gantry. Position 1 is a solo driver, position 2 is two occupants, and position 3+ is three or more. Overhead sensors read the setting as you pass and apply the matching rate.1Bay Area FasTrak. Using Your FasTrak Flex Toll Tag FAQs
The switch clicks into each position so highway vibration won’t nudge it. Set it before you start driving, or at least before you enter the Express Lane. Fumbling with it as you merge is unsafe, and a switch caught between positions can be misread by the gantry above you.
Motorcycles and Two-Seater Vehicles
Two groups get a rule that surprises new users. Motorcycles and two-seater cars carrying two people must both set the switch to 3+, not 2.2Bay Area FasTrak. Carpooling Guide The toll system treats these vehicles as carpool-equivalent, and only the 3+ setting triggers the discount they qualify for. A two-seater set to position 2 would be billed as an ordinary two-person carpool and miss the full exemption.
Where the Setting Changes Your Toll
Two kinds of facilities read the switch: Express Lanes and state-owned toll bridges. The rules and savings differ between them.
Express Lanes
In the Bay Area, corridors that read the Flex include I-580, SR-237, I-680 Sunol, I-680 Contra Costa, I-80, I-880, 101 San Mateo, and 101/SR-85 Santa Clara.1Bay Area FasTrak. Using Your FasTrak Flex Toll Tag FAQs The carpool discount varies by route:
- On I-580, two or more occupants travel free.
- On SR-237, I-80, I-880, 101 San Mateo, and 101/SR-85, two occupants pay half the posted toll and three or more travel free.
Solo drivers on any of these routes pay the full dynamic toll, which changes with real-time traffic. Southern California Express Lanes on the I-10 and I-15 also use the Flex for occupancy-based pricing.
State-Owned Toll Bridges
Seven state-owned Bay Area bridges honor the switch during posted carpool hours: Antioch, Benicia-Martinez, Carquinez, Dumbarton, Richmond-San Rafael, San Francisco-Oakland Bay, and San Mateo-Hayward. Carpools of three or more, two-seaters with two people, and motorcycles get a 50% discount when the Flex is set to 3+ and the vehicle is driven in the marked carpool lane.2Bay Area FasTrak. Carpooling Guide A standard transponder will not trigger the reduced rate even with a full car.
Getting a Flex Transponder
Order online through the FasTrak website or pick one up at Costco or Walgreens locations across California. You will need your vehicle’s license plate, make, and model, plus a payment method for the account.
Each tag requires a $25 prepaid toll balance to start. A $5 refundable security deposit applies per tag, but FasTrak waives the deposit on up to three tags per account if you set up automatic credit card replenishment.3Bay Area FasTrak. Get FasTrak If you already have a standard FasTrak account, request the Flex upgrade through your online account or by phone. Choose the Flex model explicitly at checkout; the standard tag ships by default.
Mounting the Tag
Wipe the inside of the windshield near the rearview mirror with rubbing alcohol before applying the adhesive strips. Mount the transponder directly behind the mirror, high on the glass, with the switch facing you so you can reach it and the face of the unit against the windshield. Press firmly for about 15 seconds to let the adhesive set.
California Vehicle Code Section 23302 requires that an electronic toll device be placed where it can be seen when the vehicle is on a toll facility.4California Legislative Information. California Vehicle Code VEH 23302 The behind-the-mirror position satisfies that rule and stays clear of the driver’s sightline.
Metallized Windshields
Some vehicles have a metallic oxide layer in the windshield that blocks the transponder signal. Check your owner’s manual if reads are inconsistent. Certain metallized windshields have a small clear cutout designed for a transponder; if yours doesn’t, you may need a headlamp-mounted sticker transponder that attaches to the front of the vehicle.5The Toll Roads. FasTrak Sticker Installation Instructions
Motorcycles
Riders have more flexibility. California law allows the transponder to be carried in a pocket, inside a cycle net over the gas tank, in a glove or storage compartment, mounted on a license plate bracket provided by the toll operator, or on the motorcycle’s windshield.4California Legislative Information. California Vehicle Code VEH 23302 Any of those placements work as long as the gantry can read the signal.
Do Not Cheat the Switch
Setting the toggle to 3+ while driving alone is treated as a violation, not clever pricing. Enforcement today relies on California Highway Patrol officers patrolling Express Lanes and visually counting occupants.6San Bernardino County Transportation Authority. New Technology Introduced on Interstate 10 Express Lanes A pilot on the I-10 Express Lanes is testing camera-based automatic occupancy detection that uses imaging and artificial intelligence to count passengers as vehicles pass through the tolling point.
An HOV lane citation from CHP carries a base fine of roughly $490 for a first offense, with higher amounts for repeat violations. That fine is separate from any toll adjustment the toll agency issues, so one misdeclaration can produce both a ticket and a corrected charge.
Clean Air Vehicle Discounts Have Ended
If you had a FasTrak CAV transponder that gave discounted tolls to eligible electric and hybrid vehicles, that program ended October 1, 2025. Clean air vehicles no longer receive toll discounts on Bay Area Express Lanes or the seven state-owned bridges. Existing CAV tags were automatically converted to standard FasTrak Flex tags, so they still function for occupancy-based discounts.7Bay Area FasTrak. Clean Air Vehicle Discounts Being Discontinued A solo driver in a qualifying clean air vehicle now pays the same toll as any other solo driver.
Reading the Beeps and Fixing Problems
A single beep as you pass a gantry generally means the read was successful. Multiple beeps or no sound can point to a low battery, signal obstruction, or an account issue like an insufficient balance. Check your online account after a trip to confirm the correct rate was charged; transactions list the date, time, and gantry location.
FasTrak does not publish a battery life figure for the Flex. If the tag stops responding or triggers repeat errors, call the FasTrak Customer Service Center for a replacement. Return the defective unit to avoid a lost-tag fee; the swap is free when the old one comes back.
Adhesive can loosen over time, and a shifted transponder is a common cause of missed reads. If you see a charge that doesn’t match your switch position, dispute it through your online account or by phone, and remount the tag with fresh strips if the reads keep failing.