Stay in Your Lane: When Can Police Stop a Car That Has Crossed into Another Lane of Travel?

A recent decision by the Superior Court of Pennsylvania should be of interest to any driver whose tires have ever crossed into another lane of travel ― particularly if there is evidence of illegal activity in their car.

Crossing the Center Line

In Commonwealth v. Cephus, a Pennsylvania State Police trooper observed a silver Cadillac crossing over the center dotted lines dividing the two westbound lanes of Route 422 in Limerick Township. After making this observation, the trooper activated his patrol car’s dash camera, and the footage shows the Cadillac crossing over the center line three times in a 20-second period in which both of its driver’s side tires consistently remained over the center line.

Upon observing that the driver of the Cadillac was “unable to maintain its lane several times,” the trooper initiated a traffic stop. Once he approached the vehicle, the trooper immediately smelled a strong odor of marijuana emanating from the car, observed numerous air fresheners in the car, and noticed that the driver was sweating.

The driver complied with the trooper’s request to exit the vehicle and consented to a search of the car. The trooper discovered a handgun in the center console and drug paraphernalia in the vehicle.

The driver was charged with multiple firearms and drugs offenses and sought to suppress the evidence elicited during the traffic stop, arguing that he was subjected to an unlawful vehicle stop that was not justified by probable cause.

The trial court refused to suppress the evidence, and the driver was convicted of multiple crimes and sentenced to a term of five to 10 years’ imprisonment. He appealed his conviction to the Superior Court of Pennsylvania, arguing that the trial court erred in not suppressing the evidence obtained during the traffic stop.

Repeated Violations

The traffic law upon which the stop was based provides that:

A vehicle shall be driven as nearly as practicable entirely within a single lane and shall not be moved from the lane until the driver has first ascertained that the movement can be made with safety.

In finding that the trooper had probable cause to make the stop, the Superior Court placed great weight on the fact that the trooper observed the vehicle cross the center line at least four times before pulling over the driver. The trooper “observed the vehicle failing to maintain its lane on multiple occasions and stopped the vehicle only after observing repeated violations,” the court wrote.

Since the Superior Court found that the stop was lawful, the evidence derived from it was admissible at trial, and the driver’s conviction will stand.


The ruling, obviously, is bad news for this particular driver, who will serve a lengthy term of incarceration. However, it is not necessarily bad news for all Pennsylvania drivers, as the analysis as to whether such traffic stops are lawful is fact-specific. In its written opinion, the court notes a prior decision by the Pennsylvania Supreme Court finding that law enforcement was not justified in conducting a traffic stop after observing a vehicle cross the line by six to eight inches on two occasions for a period of a second or two over a distance of approximately one-quarter of a mile. Indeed, the court urged the legislature to provide further clarification regarding the offense of crossing into another lane of travel. Its written opinion states:

To require a police officer to count how many times a vehicle is weaving before initiating a stop can lead to tragic consequences. While there might not appear to be a safety hazard at the precise moment a police officer sees a vehicle being driven erratically, that situation can change in an instant. The current state of the law does not give realistic guidance to law enforcement.