Blue Service Sign vs. Green Guide Sign
You are westbound on a six-lane arterial in an unfamiliar Massachusetts city, looking for gasoline and then I-90 west. In the right lane, you pass a blue service sign reading GAS–FOOD–24 HRS with an arrow pointing to the next exit. A quarter mile later, a green overhead sign shows a left arrow for I-90 MASS PIKE WEST and a straight arrow for ROUTE 9 WEST. Beneath it, a white sign reads LEFT LANE MUST TURN LEFT. Your GPS, which has been slow, now says turn left in 500 feet. Traffic is heavy and you are in the right lane with a line of cars beside you. A green destination sign for a hospital points right. You need gas before the highway. You must decide whether to trust the blue sign, the green signs, or the GPS, and what to do if you cannot reach the left lane.
1. Which source should govern your lane choice, and why?
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The green overhead signs and the white regulatory sign should govern. The green sign tells you which lane leads to I-90 west, and LEFT LANE MUST TURN LEFT is a regulatory lane assignment. The blue service sign tells you that gas and food are available at the next exit, but it does not tell you that the gas station is at this intersection or which lane to use. The GPS is only an aid, and it is lagging. If you need gas first, take the next exit indicated by the blue sign, then follow signs back to I-90; do not cut across heavy traffic to chase the GPS.
2. What does the blue service sign actually tell you, and what does it not tell you?
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It tells you that gas, food, and 24-hour service are available at the next exit. It does not guarantee a particular brand, price, distance from the exit, or that the station is immediately visible. It is an informational service sign, not a route marker or a lane-direction sign. You still need to watch for the exit and for smaller signs at the bottom of the ramp.
3. If you miss the left lane and the solid white line has begun, what is the correct action?
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Do not cross the solid white line or force a last-minute lane change. Continue to the next exit and use a legal U-turn or a signed route to return. A missed exit costs minutes; a late cut across three lanes costs far more. Recheck the green guide signs after you exit, and use the route marker for I-90 to confirm direction before re-entering.