Our NSR for the fourth quarter increased by 6.5%, which marked a third consecutive quarter of accelerating organic growth and included the strong contributions from both the Americas and International businesses.
We delivered a 14.8% segment adjusted operating margin in the fourth quarter and 13.8% for the full year.
To put this performance in context, our margin in the fourth quarter is more than 600 basis points higher than in fiscal 2018.
Today, we are ahead of schedule on our plans, and we have even greater conviction in our 17% longer-term goal, which we now view as achievable rather than aspirational.
Full-year adjusted EBITDA was $830 million and adjusted earnings per share was $2.82, which marked an 11% and 31% increase respectively.
Free cash flow was $583 million and was driven by our strong earnings and continued high cash flow conversion.
We have repurchased more than $1 billion of stock since last September, or 13% of the Company.
And we have $940 million remaining under our current authorization.
We delivered $3.7 billion of wins in the fourth quarter, including a 1.2 book-to-burn ratio in the design business.
Our contracted backlog, which is a key indicator of revenue growth increased by 18% and included 4% growth in design business.
And based on our clients' strengthening funding backdrop, including benefits from the $1.2 trillion infrastructure bill in the US, we expect our backlog to continue to grow.
This includes winning significantly expanded program management and design roles in transformational projects in Saudi Arabia, such as for AlUla City and a large transportation project in Qatar, where more than 100 employees have joined AECOM from the incumbent to support this work.
In the US, the $1.2 trillion Infrastructure and Jobs Act marks a generational investment in America's infrastructure.
We've initiated adjusted EBITDA and adjusted earnings per share guidance of between $880 million and $920 million and between $3.20 and $3.40.
This reflects 8% and 17% growth at the respective midpoints.
Underpinning this growth is an expectation for another year of accelerating organic NSR growth and at least 30 basis point increase in our margins to another record high of 14.1%.
Based on our strong performance to date and the returns we expect on our investments, we are raising our long-term adjusted earnings per share guidance to at least $4.75 in fiscal 2024.
This represents a more than doubling of our fiscal 2020 earnings and a nearly 20% CAGR from 2021 to 2024.
We delivered: Accelerating NSR growth; the highest margins in our Company's history; another year of double-digit adjusted EBITDA growth; more than 30% adjusted earnings per share growth and; a seventh consecutive year of free cash flow at or above our guidance range.
In the Americas, NSR increased by 7% in the fourth quarter, including growth in both design and construction management businesses.
Contracted backlog increased by 21% to set a new record.
I should note that our awarded backlog was reduced by $1.3 billion as a result of this client only advancing the first phase of this project at this time.
The fourth quarter adjusted operating margin was 19.8%, a 290 basis point increase from the prior year to a new all-time high and reflects strong execution.
NSR increased by 6% in the fourth quarter, including growth across all of our largest regions, and backlog increased by 10%.
Our adjusted operating margin in the third quarter was 7.4%, an 80 basis point improvement from the prior year.
Fourth quarter free cash flow of $299 million contributed to full year free cash flow of $583 million.
We have now repurchased nearly 20.5 million shares since September 2020, or approximately 13% of our starting share count at an average price of approximately $51.
To that point, we expect free cash flow of between $450 million and $650 million in fiscal 2022.
Importantly, our investments in growth and innovation will continue to separate us from our peers, and we are progressing toward our 17% longer-term margin target.
For fiscal 2022, we are guiding to adjusted EBITDA of between $880 million and $920 million or 8% growth at the midpoint and adjusted earnings per share of $3.20 and $3.40 or a 17% growth at the midpoint.
We expect our MSR growth to accelerate to approximately 6% in fiscal 2022.
In addition, we project a further 30 basis points of margin expansion to 14.1% as we continue to expand our lead on the industry while investing in people, clients and innovation.
Also incorporated into our guidance is a 26% effective tax rate.
This includes our expectation to now achieve adjusted earnings per share of at least $4.75 in fiscal 2024, which is 10% above our prior projection and is nearly 20% compounded annual growth rate from 2021 to 2024.

Summary:
We've initiated adjusted EBITDA and adjusted earnings per share guidance of between $880 million and $920 million and between $3.20 and $3.40.
NSR increased by 6% in the fourth quarter, including growth across all of our largest regions, and backlog increased by 10%.
For fiscal 2022, we are guiding to adjusted EBITDA of between $880 million and $920 million or 8% growth at the midpoint and adjusted earnings per share of $3.20 and $3.40 or a 17% growth at the midpoint.