We study the introduction of a microwave link between Frankfurt and London and identify its effects on German stocks that trade in both locations using a difference-in-differences setting with French firms that trade only in London as the control group. We find that the link improves the integration between the two markets as evidenced by a reduction in arbitrage opportunities and a faster reaction in London after a trade in Frankfurt. Trading volume shifts towards Frankfurt as investors - concerned about an increase in speed dispersion vis-à-vis high-frequency traders - reduce order splitting across the two cities. The effects on market quality outcomes across stocks differ as high-frequency traders strategically utilize the speed advantage resulting from the microwave link to supply or consume liquidity. In London, mid cap stocks benefit from increased liquidity provision whereas order flow for large stocks becomes more toxic. London's increased competitiveness for mid cap stocks also translates into an increase in its information share, while Frankfurt increases its information share for large cap stocks. These results suggest that market integration differently affects investors based on their speed advantage, trading venues based on their level of competitiveness, and stocks based on their size.
SAFE Working Paper No. 430
