Marco Fugazza & Frédéric Robert-Nicoud look at the swiftness of US PTA tariff cuts:

This paper investigates the empirical relationship between cuts in MFN bound rates negotiated during the Uruguay Round of the GATT (1986-1994) and the depth and breadth of Preferential Trade Agreements signed in the aftermath of its completion. Our empirical investigation focuses on the United States using official tariff line level data. To the best of our knowledge, our paper is unique in looking at the causal relationship from multilateralism to regionalism. The existing empirical literature is exclusively looking at the relationship running the other way…

[T]he imports of goods that the US liberalises swiftly the most frequently on a preferential basis are also the goods for which it granted the boldest tariff cuts during the Uruguay Round…

In the US, resistance to preferential trade liberalisation (conditional on it taking place) cannot take the form of positive preferential tariffs for institutional reasons, as we explain in the data section of the paper. It can only take the form of delayed liberalisation. Therefore, our measure of the intensity of post-Uruguay Round preferential trade liberalisation (or ‘PTL’) for each good is the frequency at which the US grants immediate duty-free access to its market to its FTA trading partners…

We find that an increase in the tariff CUT of one percentage point is associated with an increase in the probability of the US granting immediate duty-free access to its market to all trade partners by about twenty-five percent at the sample mean. Given that the standard error for CUT in the sample is 4.34 percentage points, this is a large effect…

[W]e introduce the Uruguay Round MFN tariff rate as a control in all our regressions. The estimated coefficient is negative, implying that the US disproportionately grants duty free access to its market on a preferential basis for goods that have a low MFN tariff rate already.

The authors interpret their findings as showing a complementarity between multilateral and preferential trade negotiations.