def standardize_A(A_series):
    """Compute standardized accessibility scores. This is sometimes useful, but don't use it when comparing different modes.
    
    Args: 
        A_series(Series): Accessibility scores, with index as taz ids
    Returns: 
        Series: Standardized A scores. 
    """
    return A_series.apply(lambda x: (x-A_series.mean())/A_series.std())