Is Ambush by New Parking Sign legal unless prohibited?
<p>I came across the following NYC article from on the internets whilst researching the situation for ATX:</p>

<p><a href="https://newyorkparkingticket.com/proposed-nyc-parking-law-relieves-pain-new-parking-sign/" rel="nofollow noreferrer">https://newyorkparkingticket.com/proposed-nyc-parking-law-relieves-pain-new-parking-sign/</a></p>

<blockquote>
  <p>The original law recognized the injustice of installing a new parking sign while cars were parked in spaces regulated by the old sign, and issuing parking tickets based upon a violation of a parking sign that didn’t exist when people parked their chariots. Horrible but true.</p>
</blockquote>

<p>As per the above, in NYC, it appears that there are currently explicit laws on the books that prevent installing the sign and issuing the parking tickets on the same day/week that the sign gets installed, and/or providing an affirmative defence for issued tickets.</p>

<p>What about other jurisdictions, specifically, Austin in Travis County, in Texas?  Wouldn't an appropriate notice and grace period be required for the cars parked under the old signs (or lack thereof) provided that the new signs are respected within XX hours?  (All other local laws in ATx did seem to have similar provisions, e.g., it was widely reported that at first <a href="http://www.fox7austin.com/news/a-closer-look-at-austins-handsfree-law" rel="nofollow noreferrer">only the warning was to be given for violating the hands-free ordinance</a>.)</p>

<p>In general, you don’t need an alternative defence. It is inherent in the common law that, unless the statute is explicitly retroactive (and legislators are reluctant to go there) it cannot make illegal that which was at the time of the act, legal.</p>

<p>For example, assume the old sign had unlimited and the new sign reduces this to 2 hours. If you parked before the sign was changed you could leave your car there forever so long as you never move it.</p>

<p>The NYC law give further rights - a period of grace where the owner can rely on the old restriction as a defense, even if they parked after the sign had been changed.</p>

united-states civil-law texas regulations parking