Lane-based motion in the X- and Z- coordinate space

LaneMover.cs

using UnityEngine;

// @kurtdekker - lane-based mover
//
// To use:
// Drop this on your player object
// Move your camera to see it go into the distance (see note about 2D below)
// press PLAY
// use A and D to change lanes

public class LaneMover : MonoBehaviour
{
	private int laneNumber;

	const int MaxLanes = 3;

	const float LaneWidth = 2.0f;

	const float LaneZeroXPosition = -LaneWidth * (MaxLanes - 1) / 2.0f;

	const float LateralLaneMoveSpeed = 10.0f;

	const float ForwardPlayerSpeed = 5.0f;

	void Update()
	{
		// gather input to change lanes
		if (Input.GetKeyDown( KeyCode.A)) laneNumber--;
		if (Input.GetKeyDown( KeyCode.D)) laneNumber++;

		// now guard laneNumber to 3 lanes
		if (laneNumber < 0) laneNumber = 0;
		if (laneNumber > MaxLanes - 1) laneNumber = MaxLanes - 1;

		// where should we be for this lane?
		float laneXPosition = laneNumber * LaneWidth + LaneZeroXPosition;

		// working copy
		Vector3 position = transform.position;

		// compute desired lateral position 
		position.x = Mathf.MoveTowards( position.x, laneXPosition, LateralLaneMoveSpeed * Time.deltaTime);

		// move the player downrange (change this to position.y for 2D games!)
		position.z += ForwardPlayerSpeed * Time.deltaTime;

		// of we go (replace with Rigidbody/Rigidbody2D.MovePosition() if using physics!)
		transform.position = position;
	}
}