Bicycle Lanes
HB1451: "§ 20-171.3A. Bicycle lanes.
(a) For purposes of this section, "bicycle lane" means a portion of the roadway or a paved lane separated from the roadway that has been designated by striping, pavement markings, and signage for the preferential or exclusive use of bicyclists.
(b) Whenever a bicycle lane has been provided adjacent to a roadway, operators of:
(2) Bicyclists are required to ride in the bicycle lane except when necessary to pass another person riding a bicycle or to avoid an obstruction in the bicycle lane. However, bicyclists may ride on the roadway when there is only an adjacent recreational bicycle path available instead of a bicycle lane."
"except when necessary to pass another person riding a bicycle or to avoid an obstruction in the bicycle lane."
Yikes! There's no exception for preparing for a left turn.
Mandatory bike lane laws are unnecessary, at best. A ride right rule, whether bicycle specific or general, requires bike lane use much of the time, anyway, making a mandatory bike lane law redundant. A mandatory bike lane law that lists all the important exceptions winds up being mostly a list of exceptions.
A California law lists permitted movements from a bicycle lane:
California § 21208 Permitted movements from established bicycle lanes
(a) Whenever a bicycle lane has been established on a roadway pursuant to Section 21207, any person operating a bicycle upon the roadway at a speed less than the normal speed of traffic moving in the same direction at that time shall ride within the bicycle lane, except that the person may move out of the lane under any of the following situations:
(1) When overtaking and passing another bicycle, vehicle, or pedestrian within the lane or about to enter the lane if the overtaking and passing cannot be done safely within the lane.
(2) When preparing for a left turn at an intersection or into a private road or driveway.
(3) When reasonably necessary to leave the bicycle lane to avoid debris or other hazardous conditions.
(4) When approaching a place where a right turn is authorized.
(b) No person operating a bicycle shall leave a bicycle lane until the movement can be made with reasonable safety and then only after giving an appropriate signal in the manner provided in Chapter 6 (commencing with Section 22100) in the event that any vehicle may be affected by the movement.
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HB1451: "§(1) Motor vehicles may not block the bicycle lane to bicycle traffic and shall yield to a bicyclist in the bicycle lane before entering or crossing the lane;"
Motorists should be encouraged to merge into the bike lane before turning right (last I checked, this is what the Missouri Driver's Guide recommends). It's parking in the bike lane (or unnecessarily blocking a bike lane when not making a right turn) that should be illegal, not blocking the bike lane when making a turn. Indeed, motorists should block the bike lane to make a turn in order to discourage bicyclists from dangerous passing to the right of right-turning traffic-- a primary cause of 'right hook' accidents.