A mathematician would ask: Is a lane a closed interval or an open interval?

Is letting your wheel touch a lane boundary driving "entirely within a single lane"? It turns out there is deep disagreement among courts on this question. From State v. Neal (Idaho Oct. 15, 2014); consider, as you read this, whether the court's interpretation of the rule of lenity is sound here:

A police officer stopped Neal's vehicle for a traffic violation after the officer observed the vehicle drive onto, but not across, the white line marking the right-hand edge of the traffic lane. Upon speaking with Neal, the officer noticed signs of intoxication that ultimately led to his being charged with driving under the influence of alcohol, Idaho Code § 18-8004. Neal filed a motion to suppress evidence acquired during the traffic stop. He argued that the stop was unconstitutional because when the stop was initiated, the officer lacked reasonable suspicion that Neal had violated a traffic law or was driving while intoxicated….

The officer testified that Neal had driven on the fog line at one location and then later on the white line demarcating a bike lane. He conceded that Neal had not driven over either line. After seeing Neal drive on the line a second time, the officer initiated a traffic stop … [based on Neal's violating] Idaho Code § 49-637(1), which provides:

Whenever any highway has been divided into two (2) or more clearly marked lanes for traffic … [a] vehicle shall be driven as nearly as practicable entirely within a single lane and shall not be moved from that lane until the driver has first ascertained that the movement can be made with safety.

If a criminal statute is ambiguous, the doctrine of lenity applies and the statute must be construed in favor of the accused. But, when a review of the legislative history makes the meaning of the statute clear, the rule of lenity will not be applied….

We conclude that section 49-637(1) is ambiguous. To interpret it, we consider definitions of several words used in the statute. A "laned highway" is defined as "a highway which is divided into two (2) or more clearly marked lanes for vehicular traffic." And a "traffic lane" is defined as "that portion of the roadway for movement of a single line of vehicles." Neither definition resolves whether driving on, but not over, a line constitutes a failure to stay "within" the lane. The phrase "clearly marked lane" is insufficient to resolve this issue. One could reason that a "marked lane" is the space within the markings. One could also conclude that a "marked lane" is a lane that includes the markings. Neither reading is obviously incorrect.

Moreover, this issue is not one that confounds only Idaho courts. The Idaho statute mirrors Section 11-309(a) of the Uniform Vehicle Code authored by the National Committee on Uniform Traffic Laws and Ordinances. Because that provision was adopted by many states, numerous courts have been called upon to determine whether driving on the line violates statutes with identical or nearly identical language. This issue has vexed both state and federal appellate courts and has generated a circuit split in federal courts.

Some courts have concluded that the statute is not violated when a person drives briefly on the line. See, e.g., United States v. Colin, 314 F.3d 439, 444-45 (9th Cir.2002) (When construing the California statute, including the "as nearly as practicable," the Court held that driving on the line for ten seconds, but not crossing it, did not amount to a violation.); Edwards v. State, 143 Md.App. 155, 792 A.2d 1197, 1205 (Md.2002) (Distinguishing, but not abandoning, a prior holding that touching the white line did not violate the statute, the Court concluded that briefly crossing the centerline was sufficiently dangerous to amount to a violation.); State v. Lafferty, 291 Mont. 157, 967 P.2d 363, 366 (Mont.1998) (holding the statute is only violated by unsafe lane changes and not by driving on or over the line), abrogated on other grounds by State v. Flynn, 359 Mont. 376, 251 P.3d 143 (Mont.2011); State v. Tarvin, 972 S.W.2d 910, 912 (Tex.Ct.App.1998) (holding that driving on the line does not violate the statute, but may be a sufficient basis for a stop if the "weaving is erratic, unsafe, or tends to indicate intoxication or other criminal activity").

Other courts hold that driving on the line may constitute a violation of the statute. See, e.g., United States v. Bassols, 775 F.Supp.2d 1293, 1301 (D.N.M.2011) (collecting unreported 10th Circuit cases); State v. McBroom, 179 Or.App. 120, 39 P.3d 226, 228 (Or.Ct.App.2002). However, these cases frequently hold that the driving in the particular case was not a violation due to the "as nearly as practicable" language of the statute. In United States v. Alvarado, 430 F.3d 1305, 1308 (10th Cir.2005), for example, the Court reasoned that a reasonable driver, travelling at a lawful speed, may from time to time travel outside of his lane, but declined to hold that "a single instance of drifting onto the shoulder can never be a violation." The Court held that a fact-specific inquiry is required. See also McBroom, 39 P.3d at 229 (holding that a driver does not violate the statute when he responds to "an apparent hazard" or when he has "some other valid reason for leaving his lane"); Crooks v. State, 710 So.2d 1041, 1043 (Fla.Dist.Ct.App.1998) (where driver repeatedly drove on the shoulder, the Court held that because the driver did not travel outside of the " 'practicable' lane" and because he did not drive dangerously, the statute was not violated).

None of these constructions of the words in the statutes is unreasonable or absurd. Each court, including the magistrate and district courts in this case, rendered a reasoned decision. Where the same statutory language has yielded so many divergent interpretations, we cannot escape the conclusion that the statutory language is ambiguous.

Where the language of a statute is ambiguous, we may turn to other tools of construction. When this Court must engage in statutory construction because an ambiguity exists, it has the duty to ascertain the legislative intent and give effect to that intent. To ascertain such intent, not only must the literal words of the statute be examined, but also the context of those words, the public policy behind the statute, and its legislative history. If this additional step is insufficient to clarify the meaning of the statute we must apply the rule of lenity and construe the statute in favor of the accused.

We can easily infer, from the substance of Idaho statutes describing moving violations, that the public policy undergirding Idaho traffic laws is safety. The laws were designed to reduce traffic accidents and the concomitant deaths, injuries, and property damage. Plainly, the legislative purpose in drafting Section 49-637(1) was consistent with this general purpose. Accordingly, we conclude the statute should be construed to effectuate the legislative purpose of promoting safe driving. If it were permissible for people to drive on the line dividing lanes going the same direction, on the line demarcating bicycle lanes, or on the centerline dividing a lane from oncoming traffic, the risk of accidents will increase. Accordingly, we conclude that the statute requires that vehicles be driven between lane lines "as nearly as practicable."

In the alternative, Neal argues that we should read the phrase "as nearly as practicable" expansively, to permit minor deviations from the one's lane. As indicated above, various courts have construed this language in different ways. Compare McBroom, 39 P.3d at 229 (holding that a driver does not violate the statute when he responds to "an apparent hazard" or when he has "some other valid reason for leaving his lane") with Crooks v. State, 710 So.2d 1041, 1043 (Fla.Dist.Ct.App.1998) (discussing the " 'practicable' lane").

In our view, however, the term "practicable" is unambiguous. It is defined as "able to be done or put into practice successfully," NEW OXFORD AMERICAN DICTIONARY 1338 (2001), and as "feasible in the circumstances," BLACK'S LAW DICTIONARY 1172 (6th ed.1990). These definitions are not consistent with Neal's contention that "as nearly as practicable" creates a safe harbor permitting a person to occasionally leave his lane, without any apparent need, because doing so falls within the wide spectrum of normal driving behavior. We need not, at this juncture, describe all of the weather conditions, road conditions, behavior of other drivers, or other hazards that might justify a driver in leaving the lane. Here, there is simply nothing in the record to show that Neal left his lane because staying within his lane was not "practicable." …

We conclude that driving on the line marking the edge of a traffic lane violates I.C. § 49-637(1) absent circumstances that would make it impracticable to stay between the lines. Because the "as nearly as practicable" exception has no application to Neal's driving, the traffic stop was justified. Accordingly, Neal is not entitled to suppression of evidence.