Trying to create a sense of speeding up and slowing down in 2D

I have a scrolling background and a bus. I am trying to create the impression of the bus is slowing and speeding up.

This is what I have so far, but as you can see it jumps around a bit

 using UnityEngine;
 using System.Collections;
 public class MoveBus : MonoBehaviour
 {
     public enum OccilationFuntion { Sine, Cosine }
     public bool hasArrived = false;
     public float movementDuration = 5.0f;
     public float startPont = 0.0f;
     public void Start()
     {
         //to start at zero
         //to start at scalar value
         //StartCoroutine (Oscillate (OccilationFuntion.Cosine, 2f));
     }
 
     private void Update()
     {
         if (!hasArrived)
         {
             hasArrived = true;
             float randX = Random.Range(0f, 5);
             startPont = transform.position.x;
             StartCoroutine(Oscillate(OccilationFuntion.Sine, randX));
         }
     }
 
     private IEnumerator Oscillate(OccilationFuntion method, float scalar)
     {
         float timer = 0.0f;
         //while (true)
    
         while (timer < movementDuration)
         {
             Debug.Log(timer);
             timer += Time.deltaTime;
             if (method == OccilationFuntion.Sine)
             {
                 transform.position = new Vector3(Mathf.Sin(Time.time) + startPont * scalar, 0, 0);
             }
             else if (method == OccilationFuntion.Cosine)
             {
                 transform.position = new Vector3(Mathf.Cos(Time.time) * scalar, 0, 0);
             }
              yield return new WaitForEndOfFrame();
            // yield return new WaitForSeconds(waitBeforeMoving);
           
 
         }
         hasArrived = false;
        
     }
 
   
 }