Collision detection inconsistent - swift

Question

My collision detection is working most of the time, but sometimes one physics body will go inside the other, when they should collide. I have a car with physics and road sides with physics. The car will blow through the road sides occasionally. I'm moving the car forward by position, however I have also tried moving forward by force and the same thing happens. Does anyone have any idea what would be causing this?
I've defined my physics categorys like so;
struct PhysicsCategory: OptionSet {
let rawValue: UInt32
init(rawValue: UInt32) { self.rawValue = rawValue }
static let CarCategory = PhysicsCategory(rawValue: 0b00001)
static let RoadSidesCategory = PhysicsCategory(rawValue: 0b00010)
static let NoCollisionsCategory = PhysicsCategory(rawValue: 0b00000)
}
Giving the car physics like so;
func giveCarPhysics(physics: Bool) {
//give physicsBody to the car and set to collide with the background
if physics {
self.size = CGSize(width: self.size.width, height: self.size.height)
self.physicsBody = SKPhysicsBody(rectangleOf: CGSize (width: self.size.width * 0.6, height: self.size.height * 0.9), center: CGPoint(x: self.anchorPoint.x, y: self.anchorPoint.y + self.size.height / 2))
self.physicsBody?.mass = vehicleMass
self.physicsBody?.usesPreciseCollisionDetection = true
self.physicsBody?.friction = 0.5
self.physicsBody?.restitution = 0.2
self.physicsBody?.affectedByGravity = false
self.physicsBody?.isDynamic = true
self.physicsBody?.linearDamping = airResistance
self.physicsBody?.categoryBitMask = PhysicsCategory.CarCategory.rawValue
self.physicsBody?.collisionBitMask = PhysicsCategory.RoadSidesCategory.rawValue
self.physicsBody?.contactTestBitMask = PhysicsCategory.RoadSidesCategory.rawValue
}
}
And then giving the road sides physics;
func createPhysicsRight() {
for (index, backgroundImageRight) in self.physicsRight.enumerated() {
let roadSpriteR = SKSpriteNode()
roadSpriteR.anchorPoint = CGPoint(x: 0.5, y: 0.5)
roadSpriteR.position = CGPoint(x: 0, y: CGFloat(self.physicsCounterR) * self.frame.size.height)
roadSpriteR.zPosition = 0
roadSpriteR.name = "RoadR \(index)"
print(roadSpriteR.name as Any)
roadSpriteR.physicsBody = SKPhysicsBody(polygonFrom: backgroundImageRight)
roadSpriteR.physicsBody?.mass = backgroundMass
roadSpriteR.physicsBody?.affectedByGravity = false
roadSpriteR.physicsBody?.isDynamic = false
roadSpriteR.physicsBody?.categoryBitMask = PhysicsCategory.RoadSidesCategory.rawValue
roadSpriteR.physicsBody?.collisionBitMask = PhysicsCategory.CarCategory.rawValue
roadSpriteR.physicsBody?.contactTestBitMask = PhysicsCategory.CarCategory.rawValue
roadSpriteRArray.append(roadSpriteR)
}
}
func createPhysicsLeft() {
for (index, backgroundImageLeft) in self.physicsLeft.enumerated() {
let roadSpriteL = SKSpriteNode()
roadSpriteL.anchorPoint = CGPoint(x: 0.5, y: 0.5)
roadSpriteL.position = CGPoint(x: 0, y: CGFloat(self.physicsCounterL) * self.frame.size.height)
roadSpriteL.zPosition = 0
roadSpriteL.name = "RoadL \(index)"
roadSpriteL.physicsBody = SKPhysicsBody(polygonFrom: backgroundImageLeft)
roadSpriteL.physicsBody?.mass = backgroundMass
roadSpriteL.physicsBody?.affectedByGravity = false
roadSpriteL.physicsBody?.isDynamic = false
roadSpriteL.physicsBody?.categoryBitMask = PhysicsCategory.RoadSidesCategory.rawValue
roadSpriteL.physicsBody?.collisionBitMask = PhysicsCategory.CarCategory.rawValue
roadSpriteL.physicsBody?.contactTestBitMask = PhysicsCategory.CarCategory.rawValue
roadSpriteLArray.append(roadSpriteL)
}
}